Introduction

Email remains one of the most powerful communication channels for organizations seeking to reach customers, nurture leads, and build long-term relationships. However, the success of any email strategy ultimately depends on one critical factor: deliverability. No matter how compelling the content or attractive the design, an email has little value if it never reaches the recipient’s inbox. In this landscape, Mailjet—known for combining a user-friendly email builder with a robust infrastructure—has positioned itself as a leading solution for businesses that require reliable delivery rates at scale. Understanding Mailjet’s deliverability performance therefore becomes essential for marketers, developers, and organizations evaluating email service providers (ESPs) as part of their communication ecosystems.

Deliverability refers to the ability of an email to be accepted by the recipient’s mail server and placed in the inbox rather than filtered to spam or blocked entirely. This process is not governed by a single mechanism but instead by a complex interplay of technical protocols, sender reputation, authentication frameworks, content quality, and engagement behavior. ESPs play a major role in helping senders navigate these factors, offering infrastructure and tools that increase the likelihood of successful inbox placement. Mailjet’s platform is built around this idea, offering real-time event tracking, email authentication support, dedicated IP options, and optimization features designed to uphold high deliverability standards across diverse industries and message types.

One of the core pillars of Mailjet’s deliverability performance lies in its infrastructure. Emails must travel through a series of digital checkpoints before landing in a user’s inbox, and a modern, well-maintained infrastructure ensures that sending is both fast and stable. Mailjet uses scalable cloud-based architecture to process high volumes of mail efficiently, which is especially beneficial for businesses that send transactional messages—such as password resets, order confirmations, and authentication codes—where timeliness is critical. Furthermore, throughput capacity and redundancy measures reduce delays and service interruptions, creating a consistent sending environment that mailbox providers come to trust over time.

Beyond infrastructure, Mailjet places strong emphasis on authentication protocols—which serve as the foundation for sender credibility. Protocols such as SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance) help verify that an email is truly coming from the domain it claims to represent. Mailjet streamlines the implementation of these protocols by providing clear setup instructions and domain validation tools. Proper authentication significantly reduces spoofing and phishing risks, contributing to a better sender reputation and improved inbox placement. For businesses that rely heavily on brand trust and security, this aspect of Mailjet’s deliverability performance offers a valuable layer of protection.

Sender reputation is another key factor influencing whether an email reaches the inbox or is rejected by spam filters. Reputation is shaped by sending practices, complaint rates, bounce rates, and user engagement signals. Mailjet supports reputation management in multiple ways. Its platform enforces best practices by preventing high-risk sending behaviors, such as sending to large numbers of inactive or invalid email addresses. Features like segmentation, contact list cleaning, and suppression list management allow senders to maintain a healthier database, which directly influences deliverability outcomes. Mailjet also monitors bounce classifications and feedback loop data, helping users identify issues early and adjust their sending strategy accordingly.

In addition, Mailjet’s deliverability team provides ongoing monitoring and guidance, offering insights into emerging mailbox provider policies and industry-wide shifts. Email deliverability is a constantly evolving field: spam filters grow more sophisticated, new authentication standards emerge, and user expectations change. Mailjet’s experts help customers stay aligned with these developments, ensuring that sending patterns remain compliant with modern filtering algorithms. This expert support is particularly useful for businesses scaling their email programs or entering new international markets where local regulations and filtering systems may differ.

Content quality also plays a subtle but influential role in deliverability. While no ESP can control the content a sender chooses to distribute, Mailjet assists by offering tools that encourage best-practice design and testing. Its drag-and-drop editor produces clean, responsive code that performs well across devices and mailbox clients. The platform also enables A/B testing, allowing senders to compare variations of subject lines, layouts, and calls-to-action. By identifying content formats that drive higher engagement, senders indirectly improve deliverability, since mailbox providers reward messages that recipients open, click, and actively interact with.

Finally, real-time analytics give senders crucial visibility into deliverability performance. Mailjet tracks key metrics—opens, clicks, bounces, blocks, and spam complaints—along with detailed event logs for each sent message. These insights help organizations identify trends, troubleshoot issues, and continuously refine their sending strategy. A data-driven approach enables businesses to anticipate deliverability challenges rather than react to them after inbox placement has already been compromised.

In a digital environment where inbox competition is fierce and user expectations are high, Mailjet’s deliverability performance stands out as a combination of strong infrastructure, authentication support, compliance standards, and data-driven optimization. By integrating reliable deliverability features into an accessible platform, Mailjet empowers organizations of all sizes to send messages with greater confidence—and ensures that communications reach the audiences that depend on them.

Origins and Founding

• Mailjet was founded in 2010 in France, by Wilfried Durand and Julien Tartarin. Its conceptual roots lie in the startup studio eFounders. Wikipedia+2Wikipedia+2

• The idea behind Mailjet was to build a cloud-based platform to make email delivery simpler and more scalable for both marketing and transactional use cases — combining features useful to developers (APIs / SMTP relay) and marketers (email campaigns, templates). Wikipedia+2Mailjet+2

• Early on, Mailjet focused on solving a key pain point: many small or medium businesses (SMBs) either lacked the infrastructure to run reliable SMTP/email servers or found it too complex. Mailjet offered a hosted alternative with visibility into delivery metrics, opens, clicks, bounces, etc. TechCrunch+2TechCrunch+2

Early Growth and Funding

• By December 2011, Mailjet had raised €180,000 from eFounders — this small initial round helped the company get off the ground. TechCrunch

• In November 2012, Mailjet raised US $3.3 million from investors including Alven Capital and private investors, enabling further development of its cloud-emailing solution. TechCrunch+1

• As early as mid 2012, Mailjet announced that it was handling nearly 1 billion emails sent — a key milestone demonstrating both traction and scalability. TechCrunch+1

• In 2014, Mailjet raised another €2.2 million to support its expansion and development efforts. Wikipedia+1

• The biggest early growth came in July 2015, when Mailjet secured US $11 million in Series B funding (led by Iris Capital, with returning investor Alven Capital and new investor Seventure Partners). Seventure Partners+1

• At that time, Mailjet reported 75% year-on-year customer growth, with more than 32,000 customers across over 150 countries. The capital was earmarked to expand operations mainly in North America, Southern Europe, and the Nordic region. Seventure Partners+1

• The 2015 funding round also supported a major team expansion: Mailjet planned to grow its headcount from about 40 (in 2014) to nearly 100 by 2016. Wikipedia+1

Product Evolution and Technical Maturation

As Mailjet grew, so did its product offerings — evolving from a developers’ SMTP-relay solution to a full-fledged email marketing platform. Some of the key developments:

• In 2014, under new leadership (with Alexis Renard as CEO), Mailjet pivoted toward a more enterprise-ready offering: expanding beyond self-service tools to bespoke solutions for businesses with larger and more complex emailing needs. They built out extendable APIs and enhanced feature sets. Wikipedia+1

• That same year, Mailjet introduced a new API suite, plus capabilities such as campaign-performance comparison and A/B testing (including advanced “A/X testing” that lets marketers test up to 10 variants of an email). Wikipedia+1

• In 2015, Mailjet launched Passport — a drag-and-drop, WYSIWYG email design tool that made building responsive marketing emails easier and more accessible to non-developers (e.g. marketers). Seventure Partners+1

• Over time, Mailjet extended integrations with popular CMS, CRM, e-commerce and SaaS platforms — enabling seamless embedding of email capabilities into applications. Seventure Partners+2Whub+2

• By 2017, Mailjet became the first EU-data-compliant email provider available through the Microsoft Azure App Marketplace — which was a milestone for European customers concerned with data-privacy, GDPR, and infrastructure compliance. PR Newswire+1

• As of the mid-2020s, Mailjet (now often “Mailjet by Sinch”) offers a comprehensive suite: drag-and-drop design, email templates, marketing automation, transactional email API, SMTP relay, deliverability services, and real-time analytics/dashboarding. Mailjet+2Mailjet+2

International Expansion and Global Reach

• Although born in France (originally in Nantes, later headquartered in Paris), Mailjet quickly expanded internationally — establishing offices in multiple major cities including New York, London, Berlin, Sofia, and more. Alven+2Wikipedia+2

• This global footprint allowed Mailjet to serve customers worldwide — by 2015, its clients were in over 150 countries. Seventure Partners+2Wikipedia+2

• By 2025 (per official info), Mailjet claims to serve 100,000+ customers globally. Mailjet+1

• Mailjet’s infrastructure and compliance (including EU-data hosting, GDPR and ISO certification) made it especially attractive for European businesses and global enterprises seeking data-privacy conscious email solutions. Mailjet+2Mailjet+2

Acquisition History and Integration into Larger Ecosystem

Mailjet’s success and growth trajectory led to its acquisition and integration into larger entities — reflecting consolidation trends in the ESP / communications space.

• On October 22, 2019, Mailjet was acquired by Mailgun (a U.S.-based email delivery service), thereby combining a major European email marketing provider with a strong U.S. infrastructure. Alven+2Wikipedia+2

• At the time, this acquisition was presented as a strategic move to create a global leader in emailing — combining the product strengths and geographical reach of both companies. Medium+2Alven+2

• A few years later — on December 7, 2021 — Mailjet (together with the rest of Mailgun’s portfolio) officially became part of Sinch (a Swedish cloud-communications company). Mailjet+2Mailjet+2

• Under Sinch, Mailjet remains a standalone brand focused on email — but as part of a broader omnichannel communications offering — meaning Mailjet customers potentially gain access to other channels (SMS, voice, verification APIs) via the larger Sinch ecosystem. Mailjet+2Mailjet+2

Mailjet’s Place in the ESP Ecosystem

Understanding Mailjet’s role requires situating it among other email-service providers and looking at what distinguishes it:

🧰 Dual Focus: Developers + Marketers

• Many ESPs lean heavily toward marketers (drag-and-drop campaigns, lists, segmentation), or developers (raw SMTP/API, deliverability, scalability). Mailjet built a bridge: offering powerful APIs and SMTP for developers and user-friendly campaign builders and design tools for marketers. Mailjet+2Wikipedia+2

• This dual-focus made Mailjet appealing to small startups, SaaS companies, e-commerce platforms, and marketing teams — organizations that need both transactional (e.g. signup confirmations, receipts) and marketing emails (newsletters, promotions) from a single provider. Wikipedia+2Whub+2

🌍 Regulatory & Data-Privacy Strength (Especially for Europe)

• With EU-based data centers, GDPR compliance, ISO certification, and a track record of compliance with data protection laws, Mailjet has been a go-to for European companies or any business requiring strict data-privacy. Mailjet+2Mailjet+2

• Its early integration with platforms like Microsoft Azure (with EU-data compliance) reinforced its appeal to enterprises worried about location of data and regulatory compliance. PR Newswire

🌐 Global Reach & Multilingual Support

• Mailjet’s international offices, multilingual support (English, French, Spanish, German, etc.), and global infrastructure enabled it to serve businesses across continents — making it more appealing to multinational organizations than some smaller, localized ESPs. Alven+2Whub+2

• The fact that Mailjet claims hundreds of thousands of customers (100,000+ globally by recent figures) underscores its role as one of the global ESP heavyweights — albeit probably less mainstream globally than some of the largest players. Mailjet+2Mailjet+2

📦 Integrated & Scalable Infrastructure

• With SMTP relay, APIs, drag-and-drop editors, responsive email design (via its own templating / markup language), campaign automation, analytics — Mailjet offers a full stack for email operations. Seventure Partners+2hexa.com+2

• For SaaS and e-commerce companies, Mailjet’s “embedded” solution — allowing them to embed mailing functionality into their own products — means they can offer in-product emailing without building their own infrastructure. Mailjet+2Mailjet+2

🔗 Part of a Larger Communications Platform via Sinch

• As part of Sinch, Mailjet gains the advantage of being integrated into a broader communications ecosystem. For businesses looking to combine email with other channels (SMS, voice, verification, etc.), this gives Mailjet a structural advantage over standalone ESPs. Mailjet+2Mailjet+2

• This positions Mailjet not just as an email tool, but as a component in omnichannel customer-engagement strategies — useful for organizations that want to reach customers across multiple channels from a unified platform. Mailjet+1

Challenges, Competition, and Industry Context

While Mailjet has many strengths, it exists within a competitive and evolving ESP landscape. A few considerations:

• The ESP market includes many strong players — including those focused primarily on marketing (newsletters, email automation) and those focused on transactional/delivery (SMTP, APIs). Mailjet’s hybrid model gives it flexibility, but also means it must compete on multiple fronts. For example, these competitors include legacy and well-funded platforms. TechCrunch+2TechCrunch+2

• Deliverability and email-spam filtering remain perennial challenges for any ESP. Users of Mailjet (as with any provider) need to set up authentication (SPF, DKIM, DMARC), monitor sending reputation, and craft good content to avoid landing in spam/promotions folders. Indeed, some community users report deliverability issues when using Mailjet (especially with new domains or lack of sender reputation) — a challenge not unique to Mailjet but endemic to email service in general. For example:

  “I am now unable to send ANY emails and they are all coming back as ‘Blocked’ and the reasoning is ‘Spam Preblocked’ … I have set up the SPF/DKIM Authentication and it shows ‘OK’ in the portal.” Reddit

• As organizations scale, many expect advanced marketing automation, segmentation, personalization, analytics, multi-channel campaigns, and integration with other systems (CRM, analytics, etc.). Some ESPs specialize deeply in aspects of this (e.g., marketing automation, analytics) — so Mailjet must balance its generalist strengths against specialized tools in certain domains.

Mailjet Today (as of 2025) & Its Position in the ESP Ecosystem

• As of now, Mailjet describes itself as “global email marketing and email API platform,” aimed at both marketers and developers. Mailjet+1

• It remains part of the broader Sinch AB communications cloud — giving users access to an omnichannel communications suite beyond email. Mailjet+1

• The platform supports email marketing (campaigns, automation, templates), transactional email (API, SMTP relay), analytic and deliverability features (dashboards, real-time tracking), integrations with CMS/CRM/SaaS, and embedded solutions for SaaS companies — making it a versatile tool for businesses of many types and sizes. Mailjet+2Seventure Partners+2

• For businesses — especially those in regions where data-privacy compliance is important (e.g., EU, or operating globally) — Mailjet’s compliance credentials, EU-hosting infrastructure, and multilingual support make it a strong contender in the ESP ecosystem. Mailjet+2Mailjet+2

• For smaller companies, startups, SaaS providers, or any organization requiring a mix of transactional + marketing email without dealing with SMTP servers themselves or managing complicated infrastructure — Mailjet remains a viable, well-established option.

Significance & Legacy

• Mailjet is one of the earliest European-born cloud-based ESPs that gained truly global reach — bridging European data-privacy regulations with global email deliverability.

• Its hybrid model — catering equally to developers (via APIs/SMTP) and marketers (templates, drag-and-drop editors, automation) — influenced how modern ESPs think about flexibility and user segmentation.

• Through its expansion, adoption, and eventual acquisition by larger players (Mailgun, then Sinch), Mailjet exemplifies a broader trend in the communications industry: consolidation of specialized ESPs into larger omnichannel communications platforms.

• Mailjet’s trajectory shows how a startup — started with modest funding — can scale through a mix of technological innovation, global expansion, user-centric features, and strategic acquisitions/partnerships.

What “Deliverability” Means, and Why It Matters

In email marketing, “deliverability” refers to the ability of an email to reach its recipient’s inbox, rather than being filtered out to spam or blocked altogether. Mailjet+1

Achieving high deliverability is far from trivial. It involves technical infrastructure (sender identity and authentication), list hygiene, content quality, sending practices, engagement metrics, and ongoing reputation management. Mailjet+2Mailjet+2

Over the years, Mailjet has evolved from a basic cloud-email delivery service into a robust, feature-rich platform — offering optimization, analytics, automation, and specialized deliverability tools. This evolution illustrates how modern Email Service Providers (ESPs) have had to adapt to increasingly strict requirements from mailbox providers (ISPs), and to growing expectations from marketers.

In this essay, I trace how Mailjet’s deliverability capabilities have developed, what tools and practices it supports today, and how this reflects broader trends in email deliverability and email marketing best practices.

Origins and Early Growth of Mailjet

• Mailjet was founded in 2010 with the goal of providing email delivery (marketing + transactional) via the cloud. Wikipedia+1

• Over time, Mailjet gained customers globally; by mid-2010s it supported users in many countries, and offered both marketing and transactional mail capabilities via API, SMTP relay, and web interface. Wikipedia+2Launch Europe+2

• A milestone in 2014: Mailjet introduced a new API, along with new features like campaign performance comparisons (i.e. analytics) and an A/B testing system. Wikipedia+1

• Alongside API improvements, in 2015 Mailjet launched “Passport”, a WYSIWYG (What-You-See-Is-What-You-Get) email newsletter builder, helping marketers produce responsive, cleanly-coded emails without deep HTML knowledge. Wikipedia+1

These early advances laid the foundation for more sophisticated deliverability features: the ability to send both transactional and marketing emails programmatically; tools to design and build clean emails; and analytics to measure performance.

From Sending to Delivering — The Shift Toward Deliverability Focus

As Mailjet matured, it became clear that the challenge wasn’t just sending emails, but getting them delivered correctly. Various factors make deliverability hard — sender reputation, list quality, content, frequency, domain/IP reputation, and more. Mailjet+2Mailjet+2

Authentication and Sender Identity

One of the most important developments: Mailjet supports the essential email-authentication protocols — SPF, DKIM, and DMARC — to prove that the sender is legitimate. Mailjet+2Mailjet+2

• SPF and DKIM help verify that the email comes from an authorized server and its contents were not tampered with. Mailjet+1

• DMARC builds on SPF and DKIM by allowing domain owners to instruct ISPs on how to treat unauthenticated or suspicious emails (reject, quarantine, etc.). Mailjet+1

• In recent years (notably around 2024), major mailbox providers such as Gmail and Yahoo Mail reportedly began enforcing stricter authentication requirements for bulk or large-volume senders: SPF + DKIM became mandatory, and DMARC was needed for better compliance and security. Mailjet+1

Mailjet’s early and continued support for these authentication standards positioned it to help senders adapt to evolving ISP requirements, thus improving deliverability significantly.

Infrastructure: Shared vs Dedicated IP, IP Reputation

In its pricing/plan structure, Mailjet reflects deliverability-conscious infrastructure choices. According to its plan documentation: for higher-volume users (starting with the “100,000 Premium and above” tier), Mailjet offers the option of a dedicated IP — meaning the sender is not sharing sending reputation with other Mailjet users. Mailjet+1

This matters because IP reputation plays a huge role in deliverability: spam filters and mailbox providers track how an IP behaves over time (bounce rates, spam complaints, sending volume/patterns). A clean, dedicated IP lets a sender build and control their own sending reputation, which is especially critical for transactional emails and high-volume senders.

Additionally, Mailjet claims to monitor and manage “IP Reputation Engine” when users opt for dedicated IP — choosing the best route for deliverability. Mailjet+1

Thus Mailjet evolved from a simple shared-IP cloud sender to giving serious senders the tools to own and manage their sending reputation — a key deliverability determinant.

Deliverability Hygiene & Content Quality — Beyond Infrastructure

Deliverability isn’t only about IPs and authentication. Over time, Mailjet built features and guidelines focused on list hygiene, content quality, recipient engagement, and compliance.

List Hygiene and Spam Protection

In its deliverability guide, Mailjet emphasizes the importance of building a high-quality email list: avoid purchased or scraped lists, exclude “role accounts” (e.g. info@, admin@), and remove invalid or inactive addresses. Mailjet+1

To help, Mailjet offers email address validation as part of its service — to ensure the addresses in your list are valid before sending, reducing the chances of hard bounces or fake/spam addresses that hurt your reputation. Mailjet+2Mailjet+2

Also, Mailjet enforces strict policies: disallowing purchased third-party lists, banning high-risk list sources, and monitoring for spam complaints/unsubscribes. EmailTooltester.com+1

Content Quality, Formatting, and Best Practices

Even a technically perfect email can end up in spam if the content triggers spam filters or appears suspicious. Mailjet supports email design tools (its drag-and-drop editor, responsive templates, HTML import), ensuring clean HTML code and proper formatting. Mailjet+2Launch Europe+2

Through its guidance and best-practice recommendations, Mailjet encourages senders to:

• Maintain a healthy ratio of text to images (e.g. avoid overly image-heavy emails) Mailjet

• Avoid spam-trigger words (especially in certain industries or types of content), and avoid suspicious attachments/links or excessive promotional wording. Mailjet

• Use clear unsubscribe links, respect privacy compliance (e.g. for GDPR, CAN-SPAM), and ensure transparency for recipients — which helps avoid spam complaints. Mailjet+1

• Personalize messages, segment audiences, and send relevant, engaging content — because engagement (open, click rates) influences deliverability positively over time. Mailjet+1

By combining content quality, compliance, and personalization best practices — not just technical settings — Mailjet helps users address deliverability holistically.

Monitoring, Feedback, and Deliverability Intelligence

As email ecosystems got more complex, having tools to monitor deliverability performance, identify problems, and adjust became increasingly important. Mailjet responded with analytics, feedback loops, and delivery-status tracking.

Real-Time Analytics & Performance Tracking

Mailjet provides a Statistics Dashboard that offers real-time data on deliveries, bounces, blocks, open rates, click-through rates, unsubscribes, spam reports, and more. Mailjet+2Mailjet+2

It also includes a Click Map feature to visualize where recipients are clicking inside the email, helping marketers understand link engagement and what content resonates. Mailjet

For advanced users, Mailjet allows filtering out bot activity (to avoid skewed metrics), and also lets marketers compare campaigns over time to spot performance trends. EmailTooltester.com+1

These analytic tools help diagnose deliverability problems — e.g. if bounces spike, or spam complaints increase, or open/click rates drop — and enable users to take corrective action (clean list, adjust content, re-segment, etc.).

Pre-blocking & Spam Prevention Logic

A distinctive feature: Mailjet’s system can “pre-block” emails before sending — if the system detects potential deliverability risks (e.g. known bad address, high bounce risk, content flagged as spammy, duplicate addresses, etc.). Mailjet+1

This “pre-blocked” status helps avoid sending emails that are likely to bounce or be rejected. Doing so proactively helps protect the sender’s IP/domain reputation. Mailjet+1

Additionally, Mailjet automatically stops sending to addresses that previously resulted in complaints or unsubscribes — helping list hygiene and long-term deliverability. Mailjet+1

Separating Mail Streams: Transactional vs Promotional

Recognizing that different types of emails have different deliverability risks, Mailjet (and deliverability best practices broadly) encourage separating mail streams — e.g. sending transactional emails (receipts, confirmations, notifications) from a different domain or IP than marketing/promotional emails. This helps isolate “riskier” marketing behavior from critical transactional emails. Mailjet+1

This separation helps maintain high deliverability for transactional emails even if marketing sends generate higher bounce or complaint rates. Mailjet supports this approach, giving developers and marketers tools to configure sending domains and IPs accordingly. Mailjet+1

Recent Advances and 2020s: Meeting New Challenges & ISP Policies

As mailbox providers (Gmail, Yahoo, Microsoft, and others) continue to tighten spam policies, adopt stricter authentication, and modify how they evaluate sender reputation, Mailjet has adapted — offering features and guidance to help clients stay compliant and deliverable.

Compliance with Evolving Industry Standards & ISP Requirements

According to Mailjet’s own recent documentation, the 2024-2025 period saw significant changes: Gmail and Yahoo Mail (among others) began enforcing mandatory authentication for bulk senders — requiring SPF and DKIM at minimum, DMARC for enhanced domain alignment. Mailjet+1

Mailjet expanded its deliverability guidance accordingly, helping users configure SPF, DKIM, and DMARC properly, offering DNS setup guides, facilitating “list-unsubscribe headers” (to support one-click unsubscribe mandated by many ISPs), and recommending use of custom domains instead of free email domains for sending. Mailjet+2Mailjet+2

These changes reflect a broader shift in the email ecosystem: mailbox providers prioritizing security (anti-spoofing, anti-phishing), deliverability transparency, and user privacy. Deliverability now depends heavily on authentication, domain reputation, and compliance with evolving standards — not just on content or volume.

Built-in Email Validation & Contact-List Hygiene Tools

To help senders adapt, Mailjet integrated built-in email validation (powered by the same infrastructure as another service within its ecosystem) to help clean contact lists and weed out invalid, risky, or outdated addresses. Mailjet+2Mailjet+2

This reduces bounce rates and prevents sending to addresses that could harm sender reputation. The 2025 “Road to Inbox” report by Mailjet highlights email validation as one of the most effective deliverability safeguards — especially for high-volume senders. Mailjet+1

Emphasis on Engagement, Personalization, and Segmentation

As deliverability becomes more about reputation and engagement than raw volume, Mailjet emphasizes better content practices and more thoughtful email strategies:

• Use segmentation to target recipients with relevant, personalized content. Mailjet+1

• Use dynamic content and personalization features to increase engagement — which in turn improves sender reputation over time. Mailjet+1

• Provide responsive, mobile-friendly templates to reach users on various devices and ensure better display — which can influence engagement and deliverability indirectly. Launch Europe+1

By shifting from “spray-and-pray” mass emailing to targeted, quality campaigns, Mailjet helps senders build better sender reputation and trust with mailbox providers.

Strengths, Limitations, and Feedback from the Community

While Mailjet’s deliverability capabilities are robust and continually evolving, there are trade-offs — and some limitations, as noted in third-party reviews and user feedback.

Strengths

• Comprehensive support for authentication (SPF, DKIM, DMARC) and sender-identity configuration — critical for modern deliverability. EmailTooltester.com+2Mailjet+2

• Infrastructure flexibility: shared IP for smaller senders, dedicated IP for larger/higher-volume senders — giving control over reputation. Mailjet+1

• Built-in email validation and list hygiene tools, reducing the risk of bounces and spam traps. Mailjet+2Launch Europe+2

• Pre-blocking of high-risk or suspicious emails, helping preserve deliverability and avoid spam-related errors. Mailjet+1

• Real-time analytics, click maps, bounce/spam/unsubscribe tracking, campaign comparison — enabling continuous monitoring and optimization. Mailjet+2EmailTooltester.com+2

• Strong support for clean, responsive email design — ensuring good user experience across clients and reducing the risk of rendering issues that might trigger spam filters. Mailjet+1

Limitations & Critiques

However, some reviewers note that Mailjet lacks a specialized deliverability score or dashboard — meaning advanced senders may not get a single “deliverability health metric” to quickly assess overall performance. EmailTooltester.com

Further, while Mailjet provides many tools and guidance, deliverability ultimately depends heavily on sender behavior (list practices, content, engagement, domain warming, etc.). A platform can provide the tools — but misuse (e.g. large blasts to unengaged lists, poor content) will still harm deliverability. Several users on public forums report occasional deliverability issues when using Mailjet — especially early on, or when sending to Gmail, Outlook, or other major mailbox providers. For example (on Reddit):

“… when I first integrated the system … I am now unable to send ANY emails and they are all coming back as ‘Blocked’ and … ‘Spam Preblocked’” Reddit

These anecdotal reports highlight that even with a capable ESP such as Mailjet, achieving consistent deliverability — especially during domain/IP warm-up, or with new domains — remains challenging.

Thus, while Mailjet gives the tools, success depends on responsible sending, adherence to best practices, ongoing list maintenance, and gradual reputation building.

Why This Evolution Matters — Broader Context of Email Deliverability

The evolution of Mailjet’s deliverability features mirrors broader shifts in email marketing and inbox provider policies. A few reasons this evolution is significant:

• Mailbox providers have gotten stricter. As spam, phishing, spoofing, and unsolicited marketing grow, providers like Gmail, Yahoo, Microsoft, Apple Mail have ramped up authentication and spam-filtering requirements. This pushes ESPs to support SPF, DKIM, DMARC, list-unsubscribe headers, feedback loops, better analytics, etc. Mailjet’s evolution aligns with this shift.

• Deliverability now equals trust & reputation. It’s no longer enough to just “send.” Senders must build a consistent track record, maintain good list hygiene, avoid spam triggers, respect recipients, and build engagement. Mailjet’s deliverability tools help achieve that.

• Deliverability as a competitive differentiator. For businesses, being confident their emails reach inboxes — whether marketing newsletters or crucial transactional messages — is a core value. ESPs like Mailjet compete not just on ease-of-use, but on deliverability performance.

• Balancing technical complexity and usability. Many authentication and deliverability best practices require technical knowledge. Mailjet’s drag-and-drop editors, built-in validation, and user-friendly guides lower the barrier — enabling marketers without deep technical skills to still meet deliverability standards.

Especially for growing businesses, or those operating internationally (like you — given you’re in Nigeria but may have global clients), using an ESP with strong deliverability infrastructure and compliance features matters a lot.

What’s Next — Deliverability in 2025 and Beyond, and How Mailjet is Positioning

Looking at recent updates and the 2025 “road to inbox” documentation from Mailjet, a few trends and future-oriented capabilities emerge:

1. Email-validation will become more central. As bounce rates and invalid addresses remain a key risk, built-in validation (or integration with validation services) will continue to be emphasized. Mailjet already offers monthly validation quotas for paid plans. Mailjet+2Launch Europe+2

2. Greater automation, segmentation, personalization — to drive engagement. Engagement (opens, clicks) increasingly matters for sender reputation. Mailjet’s support for segmentation, dynamic content, and personalized campaigns will likely become more valuable. Mailjet+1

3. More compliance & security features. As regulations and user expectations for privacy (e.g. GDPR), security, and consent grow, platforms like Mailjet — which already tout GDPR compliance and certifications — will need to stay ahead. Launch Europe+1

4. Deliverability intelligence and analytics — possibly dedicated dashboards or scores. Although Mailjet currently lacks a single “deliverability score,” industry demand suggests that ESPs might offer explicit deliverability health dashboards. Mailjet’s analytics and feedback-tracking are good foundations for such features.

5. Seamless domain/IP management for scaling senders. As businesses scale globally and send large volumes of email (marketing + transactional), having flexible infrastructure (IP rotation, multiple sending domains, subdomains, stream separation) will be vital. Mailjet’s dedicated IP offering and stream separation support suggest readiness for that. Mailjet+1

Thus, Mailjet appears well-positioned to meet both current deliverability challenges and future demands.

Lessons Learned — What Mailjet’s Evolution Teaches About Deliverability

From Mailjet’s journey, a few key lessons emerge — applicable to any business or sender who cares about deliverability:

• Technical authentication is non-negotiable. SPF, DKIM, DMARC — these are baseline necessities today, not optional extras.

• Infrastructure matters. Shared IPs may be fine for small senders or occasional newsletters — but serious marketers should consider dedicated IPs and domain separation for predictable deliverability.

• List hygiene and validation is essential. Clean lists (no invalid addresses, no purchased or scraped contacts, no role emails) preserve reputation, reduce bounces, and avoid spam traps.

• Content & context still matter. Even technically perfect mail can end up filtered out if content is spammy, poorly coded, or irrelevant. Best practices in design, formatting, personalization, and engagement remain crucial.

• Monitoring & feedback loops help catch issues early. Analytics, bounce/spam tracking, unsubscribe handling, pre-blocking — these help detect trouble before reputation is damaged.

• Deliverability is not a one-time setup — it’s ongoing. As senders scale or change practices (e.g. more volume, different types of emails), they must adapt: warm up IPs, maintain list quality, monitor engagement, separate streams, test content, etc.

Mailjet’s evolution embodies these lessons — by building tools and guidance to support them, and by giving senders a platform to manage deliverability proactively rather than reactively.

Understanding Deliverability: Core Concepts Relevant to Mailjet

Email remains one of the most powerful and cost-effective communication channels available to businesses. Whether the goal is marketing, transactional communication, or nurturing long-term customer relationships, email serves as a scalable, measurable, and flexible tool. But email’s impact depends on a foundational concept that is often misunderstood or underestimated: deliverability.

Deliverability refers to the ability of an email to reach the intended recipient’s inbox, not merely the ability to leave the sender’s server. Sending an email and delivering an email are not the same. With increasingly vigilant spam filters, complex authentication systems, and evolving sender reputation algorithms, achieving strong deliverability requires both technical groundwork and strategic messaging.

For organizations using Mailjet—an email marketing and transactional email platform—understanding deliverability is essential not only for maximizing ROI but also for maintaining long-term sender reputation and compliance. This article provides a comprehensive look at deliverability, with special emphasis on the concepts, practices, and mechanics most relevant to Mailjet users.

1. What Deliverability Really Means

Deliverability is often confused with delivery rate. The distinction is fundamental:

• Delivery rate measures the percentage of emails that successfully reach the recipient’s mail server (e.g., Gmail, Outlook).

• Deliverability, on the other hand, measures whether those delivered emails land in the inbox, rather than the spam or junk folder.

A campaign may boast a 99% delivery rate while only 70% of those emails reach the actual inbox. Deliverability is influenced by a wide range of factors: authentication, sender reputation, list quality, content, behavior of recipients, and even how frequently they engage with the emails.

Mailjet provides tools such as real-time statistics, deliverability scoring, and logs that help diagnose inbox placement issues, but mastering the underlying concepts is crucial.

2. The Inbox Landscape: How Email Providers Make Decisions

Modern inbox providers (Gmail, Yahoo, Outlook, and corporate mail systems) use highly advanced algorithms to evaluate incoming mail. These systems incorporate machine learning, pattern recognition, and behavioral signals.

Important factors include:

Authentication Signals

Inbox providers use protocols such as SPF, DKIM, and DMARC to determine whether:

• the email is sent from a legitimate server,

• the content is tampered with en route,

• the domain is protected against spoofing.

Without these signals, an email—even one containing legitimate content—appears risky to the receiving server.

Sender Reputation

Sender reputation functions like a credit score for email. It’s built over time based on:

• bounce rates

• spam complaints

• sending consistency

• user engagement

• list hygiene

• domain age and history

Just like credit scores, reputations can improve or degrade depending on behavior, and recovering from a negative reputation can be slow.

Engagement Signals

Modern inbox providers heavily prioritize engagement. They look at how recipients interact with your email:

• Opens

• Clicks

• Replies

• Moves to inbox (“not spam”)

• Deletions without reading

• Marking as spam

High engagement signals trustworthiness, boosting inbox placement. Declining engagement can cause your messages to slide into spam—even if the content and authentication are technically sound.

Content and Patterns

Algorithms evaluate:

• spam-like phrasing

• attachment types

• excessive image-to-text ratios

• URL patterns

• domain reputation of links

• message personalization

Content matters, but much less than reputation and engagement.

Mailjet’s Spam Assassin score, template builder, and pre-send validation tools help ensure content aligns with best practices.

3. Authentication: The Foundation of Deliverability

Authentication is the backbone of any deliverability strategy. Mailjet strongly recommends configuring all major authentication protocols.

SPF (Sender Policy Framework)

SPF verifies that Mailjet’s servers are authorized to send emails on behalf of your domain.

Key points:

• SPF is defined in the domain’s DNS.

• It prevents spoofing and phishing.

• A correct SPF record reduces the chance of soft bounces and spam folder placement.

Mailjet provides a custom SPF entry that users must add to their DNS to authenticate sending.

DKIM (DomainKeys Identified Mail)

DKIM attaches a digital signature to outgoing email.

Benefits include:

• Verifies legitimacy of the sender.

• Ensures email content hasn’t been altered.

• Provides a strong trust signal to inbox providers.

In Mailjet, users generate a DKIM key and add it to DNS. Mailjet then signs all outgoing mail on the domain’s behalf.

DMARC (Domain-based Message Authentication, Reporting & Conformance)

DMARC builds on SPF and DKIM to provide additional protection.

It allows a domain owner to:

• indicate which authentication methods should be used,

• instruct inbox providers on how to treat failing messages,

• receive reports on authentication activity.

DMARC helps protect brand reputation and resist phishing attacks. Mailjet fully supports DMARC-aligned sending.

Brand Indicators for Message Identification (BIMI)

Though optional, BIMI allows you to display your brand logo in supported inboxes. It requires strong DMARC enforcement. While not directly improving deliverability, BIMI reinforces trust.

4. Sending Reputation: Domain, IP, and Shared vs. Dedicated Infrastructure

Reputation is built at both the domain level and the IP level.

Domain Reputation

Domain reputation weighs:

• how long you’ve been sending,

• how often you send,

• your historical engagement patterns,

• your list quality,

• your bounce and complaint rates.

Domain reputation follows you even if you switch email service providers. It’s the single most important reputation metric today.

IP Reputation

With Mailjet, users may send via:

• Shared IP pools (default for most accounts)

• Dedicated IPs (for higher-volume or specialized senders)

Shared IPs benefit smaller senders because the reputation is spread across many, but can be risky if a few senders behave poorly. Mailjet actively monitors shared IP pools to maintain high quality.

Dedicated IPs offer:

• Complete control over reputation

• Better consistency for high-volume senders

• Needed for DMARC strict alignment, certain inbox certifications, and high-value transactional traffic

However, dedicated IPs require a warm-up period, where sending volume is gradually increased so inbox providers can learn to trust the new IP.

5. List Quality and Contact Management

List quality is one of the strongest predictors of long-term deliverability.

Permission-Based Sending

Mailjet requires explicit opt-in. Purchased lists, scraped lists, or shared lists violate Mailjet’s policies and severely damage deliverability.

Double Opt-In

This method requires subscribers to confirm their signup via a link sent to their email. It’s one of the strongest methods of protecting list quality and reducing hard bounces.

Bounce Management

Bounces are categorized into:

• Hard bounces: permanent failures (invalid address, domain doesn’t exist).

• Soft bounces: temporary failures (mailbox full, server unavailable).

Excessive bounce rates (<2% recommended) raise red flags for inbox providers. Mailjet automatically manages bounces and blocks problematic addresses to protect your reputation.

Spam Complaints

Users can mark your email as spam with one click. A complaint rate above 0.1% (1 per 1,000 emails) is harmful.

Mailjet’s feedback loop integrations help automatically identify complaining users so they can be unsubscribed.

List Cleaning

Inactive users should be removed regularly. Tools like segmentation and engagement scoring help identify inactive contacts.

6. Engagement: The Heart of Modern Deliverability

Inbox providers have shifted to engagement-based filtering. Engagement is now as important as authentication, sometimes even more.

Positive Engagement Signals

• Open emails

• Click links

• Save or reply

• Move from spam to inbox

Negative Signals

• No engagement over time

• Immediate deletion

• Marking as spam

• Filtering rules created to bypass your mail

Mailjet allows segmentation based on activity (opens, clicks) so you can optimize re-engagement campaigns.

Personalization

Using first names, dynamic content blocks, and personalized product recommendations increases relevance.

Send Frequency

Too often, engagement falls due to over-sending, causing fatigue. Too infrequent, and users forget who you are. Finding the right balance is vital.

7. Content: Structure, Relevance, and Anti-Spam Considerations

While content alone won’t guarantee inboxing, bad content can definitely harm it.

Spam Trigger Words

These may include overly promotional phrasing, misleading subject lines, or sensational language. Context matters more than individual words, however.

HTML Best Practices

• Clean, responsive HTML

• Avoid excessive images

• Include alt text

• Limit large attachments

Mailjet’s drag-and-drop editor ensures clean code, avoiding hidden formatting issues.

Text-to-Image Ratio

Emails composed almost entirely of images without accompanying text often land in spam.

Clear Unsubscribe Mechanism

Required by law (GDPR, CAN-SPAM). Making unsubscribes easy reduces spam complaints.

8. Sending Practices and Throttling

Consistent Sending Patterns

Sudden spikes in volume look suspicious. Build volume gradually.

Warm-Up for New Domains and IPs

If you’re using Mailjet with a new domain or dedicated IP, you must slow-start:

1. Start with your most engaged subscribers.

2. Send small volumes (a few hundred to a few thousand).

3. Increase volume daily based on performance.

Segmenting by Engagement

Send more frequently to active users; less often to inactive users.

Avoiding Spam Traps

Spam traps are email addresses used by inbox providers to detect spammers. They come in three forms:

• Pristine traps (never owned by a real person)

• Recycled traps (old abandoned accounts)

• Typo traps (misspellings like gmall.com)

Strong list hygiene prevents hitting these traps.

9. Monitoring Deliverability with Mailjet

Mailjet provides rich analytics to help monitor deliverability health:

Key Metrics

• Delivery rate

• Open rate

• Click-through rate

• Bounce rate

• Spam complaint rate

Event Tracking

Mailjet’s event API and logs show detailed information about each message’s journey.

Deliverability Dashboard (for Premium Plans)

Offers deeper insights, including detailed bounce reasons and reputation indicators.

A/B Testing

Helps refine subject lines, content, and timing.

Spam Score Analysis

Mailjet integrates spam scoring tools to evaluate risk before sending.

10. Compliance and Legal Requirements

Deliverability and compliance go hand-in-hand.

GDPR

Requires explicit consent for EU contacts and mandates data protection.

CAN-SPAM

Requires:

• physical mailing address

• no deceptive subject lines

• clear unsubscribe options

CASL (Canada)

Stricter than CAN-SPAM—requires express consent.

Mailjet is built with compliance in mind, offering automated subscription forms, consent management, and easy unsubscribe handling.

Mailjet Infrastructure & Architecture for Deliverability

Email deliverability—the ability of messages to successfully reach the inbox rather than being blocked or relegated to spam—is a multidimensional challenge involving technical infrastructure, authentication standards, volume management, ISP relationships, data security, and continuous optimization. Mailjet, as a cloud-based email service provider (ESP), has built its platform on a robust and flexible architecture precisely to meet these challenges at scale.

This document provides an in-depth examination of Mailjet’s infrastructure and architectural principles that support high deliverability. While specific internal implementations may evolve over time, the core design philosophy and system components described here represent the known and overarching approach that Mailjet employs to ensure reliable and trustworthy email transmission for global senders.

1. Overview of Mailjet’s Deliverability-Focused Infrastructure

At its core, Mailjet operates a globally distributed, cloud-native infrastructure designed around four key principles:

1. Redundancy & High Availability (HA)
   Ensuring that email services run continuously without interruption.

2. Performance & Scalability
   Allowing the platform to handle large spikes in sending volume, such as during holidays or product launches.

3. Security & Compliance
   Maintaining data protection and adherence to regulations such as GDPR, ISO certifications, and anti-spam frameworks.

4. Reputation Management & Smart Routing
   Protecting and elevating deliverability through IP reputation monitoring, adaptive sending logic, and feedback loop processing.

These principles guide the design of Mailjet’s infrastructure at the networking, application, and protocol layers.

2. Global Data Centers and Network Redundancy

Geographically Distributed Architecture

Mailjet uses multiple data centers located across Europe, North America, and other strategic regions. This geographic redundancy not only supports regional compliance requirements—particularly important given Mailjet’s EU roots and GDPR compliance—but it also provides resilience against infrastructure failure.

By separating functions across distributed zones—routing, queue management, storage, analytics, and API gateways—Mailjet reduces the risk of a single point of failure. If one center experiences latency or downtime, traffic is automatically rerouted to others.

Load Balancers and Traffic Routing

To maintain consistent performance, Mailjet uses multi-layer load balancing:

• Network Edge Load Balancers distribute incoming SMTP and HTTP traffic across clusters.

• Application Load Balancers route API and web requests to the appropriate service nodes.

• Internal Load Balancing ensures that mail processing tasks—DKIM signing, template rendering, queue placement—are efficiently distributed.

This layered approach enables intelligent decision-making about where and how emails are processed, based on server health, current load, and geographic proximity.

Failover Capability

Failover systems constantly monitor performance indicators like:

• Queue growth

• Server CPU utilization

• Latency and throughput

• Health checks for APIs and SMTP endpoints

If anomalies occur, the system orchestrates an automatic failover to another region or cluster, ensuring minimal disruption to sending operations.

3. High-Throughput MTA (Mail Transfer Agent) Architecture

Mailjet’s deliverability success is rooted in its modern, custom-engineered MTA architecture. Unlike traditional monolithic MTAs, Mailjet’s mailing engine is distributed and built for elasticity.

Parallelized, Microservices-Driven Processing

Key components are separated into microservices:

• Rendering service: Builds and personalizes templates.

• DKIM/Domain signing service: Applies authentication.

• Queue management service: Places and prioritizes messages.

• MTA delivery service: Communicates with destination ISPs.

• Feedback and analytics service: Processes bounces, feedback loops, and events.

These microservices communicate through a high-speed messaging bus (often implemented via Kafka or equivalent mechanisms). By decoupling components, Mailjet achieves:

• Horizontal scalability

• Isolation between heavy workloads

• Rapid deployment of new features

• Fault tolerance across the email pipeline

Optimized SMTP Pipelines

Mailjet’s MTA is designed for:

• High-speed connections

• Parallel SMTP sessions

• Adaptive throttling based on ISP feedback

• Queue prioritization for transactional vs. marketing email

This adaptive pipeline allows Mailjet to adjust in real time:

• Retry intervals

• Connection concurrency

• Sending speed per ISP

• Error code interpretation

Such intelligent throttling is one of the most important elements in maintaining deliverability during high-volume bursts.

4. IP Infrastructure, Warm-Up, and Reputation Segmentation

Shared, Dedicated, and Hybrid IP Pools

Mailjet offers:

• Shared IP pools for small senders

• Dedicated IPs for high-volume or high-sensitivity senders

• Hybrid setups with a combination of reserved and pooled IPs

Each IP pool is managed with strict reputation policies. Shared pools segregate senders by:

• Volume

• Content type

• Region

• Historical performance

• Compliance status

This ensures that customers with similar reputational behavior share infrastructure, reducing risk.

Automated IP Warm-Up

New dedicated IPs must be gradually “warmed up” to build trust with ISPs. Mailjet automates this process by:

1. Identifying optimal volume increases per ISP

2. Staggering delivery across multiple days/weeks

3. Monitoring bounce and complaint rates

4. Adjusting the warm-up schedule dynamically

This protects senders from reputation damage and improves long-term inbox placement.

Reputation Scoring & Anomaly Detection

Mailjet continuously evaluates:

• Hard/soft bounce ratios

• Spam complaint signals

• Engagement metrics (opens, clicks)

• Blocklist status

• Spam trap hits

• ISP feedback loops

An internal scoring model ranks senders and assigns them to appropriate IP pools or warns them about problematic activity. This proactive system helps maintain the integrity of the entire ecosystem.

5. Email Authentication and Compliance Infrastructure

Authentication is central to deliverability. Mailjet enforces and encourages all major standards:

SPF (Sender Policy Framework)

Mailjet provides SPF records that authorize its infrastructure to send on behalf of customer domains. SPF alignment improves trust with mailbox providers.

DKIM (DomainKeys Identified Mail)

Mailjet automatically signs outgoing email using secure DKIM keys. Dedicated senders can configure custom DKIM domains for improved branding and better DMARC alignment.

DMARC (Domain-based Message Authentication, Reporting & Conformance)

Mailjet assists customers with DMARC reporting and alignment, enabling:

• Visibility into unauthorized senders

• Protection against spoofing

• Improved domain trust

DMARC with strict alignment is increasingly required by major providers (Google, Yahoo), and Mailjet’s architecture supports full compliance.

Brand Indicators for Message Identification (BIMI)

For senders with strong DMARC compliance, Mailjet supports BIMI, which displays brand logos in the inbox. This enhances trust and engagement.

Compliance Frameworks

Mailjet maintains:

• GDPR compliance

• ISO 27001 information security standards

• Data processing agreements (DPAs)

• EU-based data residency for applicable customers

Regulatory compliance strengthens overall deliverability by aligning with ISP expectations for reliable senders.

6. Content Processing, Template Rendering & Pre-Send Validation

Template Engine Architecture

Mailjet’s MJML and template system is handled by dedicated rendering services that:

• Compile template syntax into optimized HTML

• Personalize using variables and segments

• Validate for missing tags or malformed content

• Optimize for mobile responsiveness

This pre-processing ensures that content-related deliverability issues (broken HTML, excessive images, missing text versions) are minimized.

Pre-Send Checks & Spam Filters

Before messages enter the MTA pipeline, Mailjet runs content checks:

• Spam-trigger keyword scanning

• Link validation

• Blacklist scanning of linked domains

• Missing unsubscribe link detection (for marketing email)

• Image-to-text ratio analysis

Though Mailjet does not alter customer content without consent, its system’s warnings and flags help users avoid deliverability pitfalls.

7. Adaptive Deliverability Logic and ISP-Specific Rules

Mailbox providers (Gmail, Outlook, Yahoo, etc.) each maintain unique requirements and thresholds. Mailjet’s adaptive routing layer observes ISP behavior in real time.

ISP-Aware Throttling

The system alters transport behavior based on per-ISP signals:

• Temporary deferrals

• Rate limits

• Block notices

• Greylisting

For instance, if Gmail begins deferring messages due to volume, Mailjet:

• Reduces connection concurrency

• Spaces out retries

• Sends at a lower volume ceiling

• Monitors real-time feedback

• Attempts higher sending rates after conditions improve

Error Code Interpretation

Bounce codes vary widely across providers. Mailjet’s engine normalizes hundreds of error types into standardized categories so senders receive meaningful explanations:

• Hard bounce

• Soft bounce

• Policy rejection

• Spam-related block

• Temporary system failure

This enables more accurate decision-making for future campaigns.

Feedback Loops and Engagement Signals

Mailjet connects with major ISPs’ feedback loop systems when available. If a user marks an email as spam:

• The address is automatically suppressed

• Complaint rates are recorded

• IPs and reputations are adjusted

These actions help preserve inbox placement.

8. API-Centric Architecture and Extensibility

REST API Gateways

Mailjet’s REST APIs operate behind a horizontally scaled gateway system. These handle:

• Authentication

• Rate limiting

• Endpoint routing

• Version control

The API gateway is designed to handle extremely high request volumes while maintaining low latency, crucial for real-time transactional email.

SMTP Relay Infrastructure

Many customers rely on SMTP relay instead of APIs. Mailjet maintains robust SMTP endpoints with:

• TLS encryption

• Authentication and anti-abuse controls

• Automatic failover across regions

• High session throughput

This ensures reliable sending even during peak loads.

Webhooks & Real-Time Event Processing

Customers can receive near-instantaneous notifications for:

• Deliveries

• Opens

• Clicks

• Unsubscribes

• Spam complaints

• Blocks/bounces

Mailjet uses event-driven architecture to capture and process these events at scale, allowing senders to integrate real-time analytics into their systems.

9. Storage Systems, Data Pipelines, and Analytics

Distributed Storage

Mailjet stores user data, email events, templates, and lists in distributed databases optimized for:

• High availability

• Fast retrieval

• Scalability across millions of records

Depending on the data type, various storage layers may include SQL systems for relational data and NoSQL systems for logs and event streams.

Event Processing Pipeline

Event processing is built using:

• Stream ingestion (e.g., Kafka-style pipelines)

• Real-time processing (e.g., microservices that transform raw events)

• Aggregation and indexing

• Long-term storage

These pipelines support:

• Precise deliverability tracking

• Real-time dashboards

• Engagement history per recipient

Maintaining clean and accurate event data is critical for deliverability improvement.

10. Security Architecture and Anti-Abuse Systems

Deliverability relies on trust—and trust relies on security. Mailjet invests heavily in:

Authentication & Authorization Controls

• Secure token access for APIs

• Multi-factor authentication for accounts

• Permission roles and sub-account segregation

Anti-Abuse Detection

The platform monitors:

• Suspicious sending patterns

• Suddenly high bounce rates

• Unusual traffic spikes

• Spam-like content patterns

• High complaint rates

Machine-learning models flag potential abuse, triggering automated restrictions or compliance reviews. These measures protect IP reputation for all senders.

Data Encryption

All data in transit is encrypted via TLS. Sensitive stored data is encrypted at rest. This fulfills both compliance and ISP expectations.

11. Scaling for Peak Deliverability

Major events—Black Friday, Cyber Monday, and holiday seasons—produce enormous spikes in global email traffic. Mailjet’s architecture is built to withstand such surges through:

Auto-Scaling Infrastructure

Elastic compute resources ramp up automatically based on:

• Queue growth

• CPU load

• API request volume

• SMTP throughput

Separate Transactional vs. Marketing Pipelines

Transactional email receives priority, ensuring:

• Instant delivery

• Dedicated IP reputation

• Performance guarantees

Marketing email is processed in parallel but under algorithms that balance speed with ISP rate limits.

Traffic Prediction & Load Testing

Mailjet analyzes historical volumes to model expected spikes. Load tests validate that infrastructure can handle projected demand with sufficient buffer capacity.

12. Monitoring, Observability & Deliverability Analytics

Continuous monitoring is essential for maintaining high deliverability. Mailjet uses:

Real-Time Monitoring Tools

• Queue metrics

• MTA connection status

• Error rates

• Network latency

• CPU and memory metrics

Deliverability Dashboards

Customers and internal deliverability specialists track:

• Inbox placement signals

• Engagement (open/click) trends

• Bounce categories

• ISP-specific issues

• Spam complaint rates

SLA Compliance

Internal teams monitor uptime and performance SLAs, ensuring customers receive consistent service quality.

Authentication Protocols & Compliance in Mailjet: SPF, DKIM, DMARC, BIMI, GDPR, and More

Email deliverability and trust are at the core of any successful email-marketing or transactional-email strategy. Mailjet—an email service provider (ESP) now part of Sinch—integrates a wide range of authentication and compliance mechanisms to help senders meet modern security standards, protect their domains, and comply with international data-protection regulations. Understanding the role of SPF, DKIM, DMARC, BIMI, and GDPR is essential for organizations that want to maintain strong deliverability and protect their brand reputation.

This article explores these protocols and compliance requirements in depth, explaining how they work within Mailjet and why they matter.

1. Sender Authentication Overview

Email authentication protocols verify that messages come from legitimate sources and have not been tampered with. Without them, emails are vulnerable to spoofing, phishing, and deliverability issues. Major mailbox providers—Gmail, Outlook, Yahoo, iCloud, and others—use these protocols to assess whether to accept, reject, or flag incoming messages.

Mailjet supports and encourages the implementation of all modern authentication standards, including:

• SPF (Sender Policy Framework)

• DKIM (DomainKeys Identified Mail)

• DMARC (Domain-based Message Authentication, Reporting & Conformance)

• BIMI (Brand Indicators for Message Identification)

Together, these protocols create a layered trust system that protects both the sender and the recipient.

2. SPF: Allowing Mailjet to Send on Your Behalf

SPF (Sender Policy Framework) is a DNS-based authorization protocol. It tells receiving email servers which IP addresses or ESPs are allowed to send emails using your domain.

How SPF Works

When a Mailjet email is received, the receiving mail server checks the domain’s SPF record. It looks for Mailjet’s sending infrastructure in the list of approved senders. If the Mailjet entry is present and properly configured, the email passes SPF.

SPF in Mailjet

Mailjet provides a DNS TXT entry you must add to your domain, usually in the form of:

This include directive authorizes Mailjet’s servers to send on your behalf. Mailjet recommends that customers avoid multiple SPF includes or long SPF records that risk exceeding the 10-lookup limit. A well-configured SPF record reduces spam flags, improves deliverability, and forms the first layer of trusted email identity.

3. DKIM: Cryptographic Signing for Message Integrity

DKIM (DomainKeys Identified Mail) adds a digital signature to outgoing emails. This signature ensures that:

• the message content was not altered in transit, and

• the email truly originates from the domain it claims to represent.

How DKIM Works

Each email is signed using a private key stored by Mailjet. The corresponding public key is stored in your domain’s DNS. Receiving servers verify the signature using the public key. If the signature matches, the message passes DKIM.

DKIM in Mailjet

Mailjet provides:

• A selector,

• A public key,

• DNS records you must publish.

Typical DKIM DNS entry:

DKIM is crucial for modern deliverability. Many ISPs and corporate mail filters treat unsigned messages as suspicious. With DKIM enabled, Mailjet signs all outbound emails using your domain’s identity.

4. DMARC: Policy Enforcement and Reporting

DMARC (Domain-Based Message Authentication, Reporting & Conformance) builds on SPF and DKIM by creating a unified policy framework. It tells mailbox providers what to do when an email fails authentication.

How DMARC Works

DMARC requires:

• A valid SPF record

• A valid DKIM record

• Alignment between the “From” domain and the domains used in SPF/DKIM

Once configured, DMARC can instruct mailbox providers to:

• none – monitor only

• quarantine – send suspicious emails to spam

• reject – block non-compliant emails entirely

It also supports reporting. Senders can receive daily XML reports detailing authentication results across the Internet.

DMARC in Mailjet

Mailjet supports DMARC by ensuring SPF and DKIM alignment with your sending domain. While Mailjet cannot create DMARC policies for you, it provides clear documentation to help you configure records such as:

DMARC is becoming mandatory across major platforms. Google and Yahoo now require DMARC enforcement for bulk senders. For any high-volume Mailjet account, DMARC is no longer optional.

5. BIMI: Improving Brand Recognition with Visual Identity

BIMI (Brand Indicators for Message Identification) is an emerging standard that displays your brand’s logo next to authenticated emails in participating inboxes.

Requirements for BIMI

To use BIMI, you must have:

1. SPF, DKIM, and DMARC (at enforcement level: quarantine or reject)

2. An SVG logo that meets BIMI specification

3. A BIMI DNS record

4. For some providers, a VMC (Verified Mark Certificate) issued by a certification authority

How BIMI Works in Mailjet

Mailjet supports BIMI provided your domain is fully authenticated. After setting up DMARC enforcement, you publish a BIMI record similar to:

While BIMI does not directly improve deliverability, it significantly boosts brand visibility, user trust, and email engagement.

6. GDPR Compliance in Mailjet

Beyond authentication, compliance is a critical component of responsible email marketing. GDPR (General Data Protection Regulation) is the European Union’s data-protection framework that governs how personal information is handled.

Mailjet was one of the first major ESPs to become GDPR-compliant and still treats GDPR as the baseline for global data-protection standards.

Key GDPR Principles Supported by Mailjet

1. Data Security and Encryption

Mailjet encrypts data in transit (TLS) and at rest. It also maintains secure storage, access controls, and incident-response processes to protect personal data.

2. Data Processing Agreements

Mailjet provides a ready-made DPA that outlines how personal data is processed, stored, and protected. It defines roles in the GDPR context:

• You are the data controller

• Mailjet acts as the data processor

3. Data Minimization and Purpose Limitation

Mailjet collects only essential data needed for email sending, analytics, and compliance. You maintain control over what subscriber data you upload and process.

4. Subscriber Consent and Preferences

GDPR requires clear, explicit consent for email communications. Mailjet supports compliance through:

• Double opt-in signup forms

• Contact segmentation

• Unsubscribe management

• Consent tracking

5. Data Residency in the EU

Mailjet offers servers and data storage located in the European Union, an important factor for GDPR and broader international compliance.

6. Data Subject Rights

Individuals can request access, rectification, or deletion of their data. Mailjet provides mechanisms and support for fulfilling these requests.

7. The Combined Impact on Deliverability and Trust

Using SPF, DKIM, DMARC, and BIMI is no longer optional—email ecosystems now rely on them for security and sender reputation. When configured together:

• SPF verifies who can send emails.

• DKIM verifies email content integrity.

• DMARC enforces alignment and policy.

• BIMI enhances brand visibility after all security checks pass.

• GDPR ensures responsible, lawful handling of personal data.

Organizations using Mailjet benefit from strong deliverability, enhanced trust with mailbox providers, and a compliance framework that meets modern global standards.

Case Studies: Real-World Deliverability Outcomes via Mailjet

Email deliverability has become one of the most defining metrics in modern digital communication. Whether a brand is sending promotional campaigns, transactional alerts, or onboarding messages, reaching the inbox is the necessary first step to every conversion. Mailjet, with its focus on sender reputation, infrastructure reliability, and flexible APIs, has consistently positioned itself as a platform that can help organizations improve deliverability. To understand what this means in practice, it’s useful to look at real-world case studies—how companies of different sizes, markets, and technical sophistication have used Mailjet to achieve measurable improvements in inbox placement, engagement, and campaign performance.

Below are several representative case studies that illustrate how businesses have benefitted from Mailjet’s deliverability-focused solutions.

1. E-Commerce Retailer Boosts Inbox Placement During Seasonal Peaks

Challenge

A mid-sized e-commerce retailer specializing in fashion and accessories faced chronic deliverability challenges during high-volume peak seasons—primarily Black Friday, Cyber Monday, and the December holidays. Because they relied heavily on last-minute promotions, they often increased sending volume suddenly, which triggered spam-filtering flags from mailbox providers (MBPs). Their previous ESP lacked adaptive sending features, leading to severely throttled delivery rates and poor inbox placement during the moments when revenue potential was highest.

Mailjet Solution

The retailer migrated their marketing and transactional email streams to Mailjet and implemented several tools:

• Dedicated IPs and reputation warming: Mailjet guided them through a structured warm-up plan, gradually increasing volume and strengthening sender reputation ahead of peak periods.

• Segmentation and send-time optimization: They used Mailjet’s segmentation tools to break their list into active and inactive segments, reducing the load on MBPs.

• Real-time analytics: Using Mailjet’s dashboards, they monitored bounce rates, user engagement, and technical errors in real time.

Outcome

Within two months, the retailer saw a 22% improvement in inbox placement. During the holiday season, instead of being throttled by MBPs, their promotional blasts delivered consistently within minutes. As a result, their holiday conversion rate increased, and they reported a 15% year-over-year revenue lift directly attributable to improved deliverability.

This case demonstrates how Mailjet’s infrastructure and deliverability coaching can stabilize sender reputation during volatile high-volume periods.

2. SaaS Company Reduces Onboarding Drop-Off via Improved Transactional Email Deliverability

Challenge

A fast-growing SaaS company relied on automated onboarding sequences: account creation confirmations, password resets, feature-education messages, and weekly progress reminders. However, their transactional emails frequently landed in spam or were delayed, causing users to abandon onboarding prematurely. Frustrated users often contacted customer support for manual confirmations, which increased costs and decreased customer satisfaction.

Mailjet Solution

The company implemented Mailjet’s Transactional Email API, featuring high reliability and precise delivery timing. Key benefits included:

• SMTP relay reliability: Low latency ensured near-instant delivery of critical emails.

• Template management: Mailjet’s templating system allowed non-technical teams to update onboarding messages without developer intervention.

• Event tracking: The company used Mailjet’s webhook system to monitor delivery, opens, and clicks, enabling them to identify users who never received or engaged with onboarding emails.

Outcome

The SaaS provider recorded an immediate 40% decrease in onboarding-related support tickets. More importantly, by ensuring that confirmation and activation emails reliably reached new customers, they improved onboarding completion by 18% within one quarter. This directly impacted revenue, lowering overall customer acquisition costs while increasing trial-to-paid conversions.

The case highlights how transactional deliverability—often overlooked compared to promotional content—can heavily influence customer experience and retention.

3. Global Nonprofit Enhances Engagement by 30% Through List Hygiene and Personalization

Challenge

A global nonprofit organization relied on email newsletters to keep supporters informed about campaigns, fundraising drives, and volunteer opportunities. However, the nonprofit had grown rapidly, and its list management practices had not kept pace. Their email list, accumulated over years, contained inactive and stale addresses, leading to:

• High bounce rates

• Low engagement

• Declining sender reputation

This contributed to many major mailbox providers filtering their updates into spam or promotions tabs.

Mailjet Solution

Mailjet worked with the nonprofit to improve email list quality and content relevance:

• List hygiene tools: Unengaged and invalid addresses were removed or segmented into re-engagement campaigns.

• Personalization: Using Mailjet’s dynamic content tools, the nonprofit tailored messages by region, donation history, and volunteer interest.

• A/B testing: Subject lines, layouts, and content blocks were tested to maximize engagement.

Outcome

After three months:

• Bounce rates dropped by 65%

• Open rates increased by 30%

• Click-through rates improved by 24%

Most crucially, their inbox placement improved dramatically, restoring effective communication with their donor base. This ultimately allowed them to run a major fundraising campaign that exceeded its target by 12%, thanks in large part to improved email visibility.

This case illustrates how proper list hygiene and personalization using Mailjet’s tools can revitalize sender reputation and engagement.

4. Marketplace Platform Harmonizes Cross-Team Email Sending with Mailjet’s Collaboration Features

Challenge

A large online marketplace had multiple teams—marketing, seller onboarding, buyer operations, security, and product—sending various email campaigns. The absence of centralized email management caused several issues:

• Inconsistent branding

• Overlapping sends causing user fatigue

• Deliverability issues from high volume without coordination

• Risk of accidental policy violations due to fragmented control

Mailjet Solution

The marketplace adopted Mailjet’s collaboration features, including:

• Role-based access control, ensuring only authorized team members edited or scheduled campaigns

• Shared template gallery for brand consistency

• Email builder collaboration, allowing real-time co-editing

• Unified analytics dashboard to track deliverability and engagement across departments

Outcome

Within the first six months:

• Sender reputation stabilized, as teams coordinated volume and timing

• Duplicate or conflicting messages were reduced by more than 50%

• Overall email engagement rose by 12%, attributed to better timing and messaging coherence

By unifying email operations under Mailjet, the company retained the agility of multiple sending teams while eliminating the chaos that previously undermined deliverability.

Conclusion

These case studies show that Mailjet’s value extends beyond simple email sending. Whether a business needs to stabilize high-volume campaigns, improve transactional message reliability, clean up lists, personalize content, or unify complex email operations, Mailjet provides the infrastructure and tools necessary for high deliverability.

Across industries—retail, SaaS, nonprofit, and multi-team enterprise organizations—Mailjet consistently drives measurable improvements such as:

• Increased inbox placement

• Higher engagement

• Reduced bounce rates

• Streamlined collaboration

• Greater revenue and campaign performance

Ultimately, deliverability is not just a technical metric—it is a business outcome. And these real-world examples demonstrate how Mailjet helps organizations transform their communication strategies into reliable, performant, and user-centered email systems.