Email deliverability has declined by 8% globally in 2025, posing significant challenges for marketers aiming to reach their audience effectively. This downturn is attributed to several evolving factors in the digital landscape.
The email delivery global decline is a significant warning sign for marketers. The reported 8% drop in email deliverability is largely driven by a combination of new, stricter rules from major inbox providers and a failure by many senders to adapt to modern email hygiene and authentication standards.
Factors Contributing to the Global Decline in Email Deliverability
What’s Causing the Decline in Email Deliverability? Here are the primary causes behind the global decline in email deliverability:
1. Enhanced Spam Filtering Algorithms
Major email providers like Gmail, Outlook, and Yahoo have implemented more sophisticated spam filtering algorithms. These systems now assess not only technical aspects but also the content and engagement levels of emails, leading to stricter filtering criteria. Consequently, emails that previously landed in inboxes may now be redirected to spam or promotions folders. (Mailgun)
2. Increased Sender Authentication Requirements
To combat phishing and improve security, platforms such as Microsoft have raised the bar for sender authentication. As of May 2025, Microsoft requires senders delivering more than 5,000 emails per day to their consumer domains to implement SPF, DKIM, and DMARC with a minimum policy of p=none. Failure to comply can result in emails being blocked or filtered out. (Mailgun)
3. Deteriorating Sender Reputation
A sender’s reputation is increasingly influenced by factors like bounce rates, spam complaints, and engagement metrics. Poor sender reputation can lead to emails being filtered into spam folders, throttled delivery, or even blacklisting of the sender’s domain or IP address. (clearout.io)
4. Declining Email List Quality
Approximately 23% of an email list declines in quality each year due to factors like inactive subscribers and outdated contact information. This deterioration can lead to higher bounce rates and increased spam complaints, negatively impacting deliverability. (InboxWP)
5. Changes in Subscriber Behavior
Shifts in how subscribers interact with emails, such as increased use of mobile devices and changes in email client preferences, can affect deliverability. Emails not optimized for these behaviors may experience lower engagement, leading to higher chances of being marked as spam. (Litmus)
That global decline is a significant warning sign for marketers. The reported 8% drop in email deliverability is largely driven by a combination of new, stricter rules from major inbox providers and a failure by many senders to adapt to modern email hygiene and authentication standards.
6. New, Stricter Inbox Provider Requirements (The “Big Three” Shift)
The most impactful change has been the mandatory new rules enforced by major providers like Google (Gmail), Yahoo, and Microsoft (Outlook/Hotmail), particularly for high-volume senders.
- Mandatory Email Authentication: This is now non-negotiable. Senders are required to implement and configure all three major authentication protocols—SPF, DKIM, and DMARC—to verify their identity. Emails failing these checks are now far more likely to be sent straight to spam or outright rejected.
- Stricter Spam Complaint Thresholds: Google and Yahoo now enforce extremely low spam complaint rates (often recommending senders stay below 0.1%). A sender’s reputation is instantly and severely damaged if they cross this threshold, leading to mass filtering of all future emails into the junk folder.
- Easy Unsubscribe Requirement: Senders must implement a clear, one-click unsubscribe mechanism in the email header. Making it difficult to opt-out dramatically increases the likelihood that a user will mark the email as spam instead, which is a much harsher signal to inbox providers.
7. Heightened Focus on Engagement Metrics
Inbox providers are increasingly using user behavior as the main factor in filtering decisions, making it harder for senders with low engagement to reach the primary inbox.
- Low Open/Click Rates: Emails that are consistently ignored, deleted without opening, or which receive no clicks signal to the provider that the content is irrelevant. This actively trains the spam filters to send future emails from that sender’s domain to the spam folder.
- The Vicious Cycle: Low engagement causes more emails to be sent to spam, which further lowers engagement metrics, creating a downward spiral for the sender’s reputation.
- Negative Signals: The most damaging signals are recipients moving an email from the inbox to the spam folder or marking it as spam.
8. Poor List Quality and Hygiene
Many businesses are still clinging to outdated or inactive email lists, which instantly triggers spam filters.
- High Bounce Rates: Sending emails to addresses that are invalid, closed, or non-existent (hard bounces) is a strong indicator of a poor-quality list. Providers typically block senders who consistently exceed a low bounce rate (often around 2%).
- Sending to Unengaged/Inactive Subscribers: Continuously emailing recipients who haven’t opened, clicked, or interacted in six months or more hurts sender reputation, as it tells the ISP that the sender is “blasting” irrelevant content.
- Spam Traps: Unused, carefully placed email addresses used by ISPs to catch senders with bad list-collection or list-buying practices. Hitting a spam trap is one of the fastest ways to get blacklisted.
9. General Marketing Practices
While not new, these sender-side issues continue to damage overall deliverability:
- Overly Promotional Content & Spam Triggers: Excessive use of promotional language (e.g., all caps, too many exclamation points, keywords like “FREE! ACT NOW!”), and a poor text-to-image ratio can still trigger content filters.
- Inconsistent Sending Volume: Sudden, large spikes in email volume from a domain that usually sends a low amount can be flagged as a sign of a potential spam or malicious campaign.
- Failing to Honor Opt-Outs: Not processing unsubscribe requests quickly is not only illegal in many jurisdictions but also guarantees the recipient will mark the next email as spam, which is the most damaging thing for a sender’s reputation.
Strategies to Improve Email Deliverability
Email deliverability is a crucial concept in email marketing and communication, going far beyond simply hitting the “send” button. It is the measure of your success in getting your emails into the recipient’s inbox (as opposed to their spam folder, promotions tab, or being blocked entirely).
A high deliverability rate is the cornerstone of effective email communication, directly impacting your open rates, clicks, conversions, and ultimately, your return on investment (ROI).
- Implement Robust Authentication Protocols: Ensure SPF, DKIM, and DMARC records are correctly configured and aligned to meet the requirements of major email providers.
- Maintain a Clean and Engaged Email List: Regularly update and clean email lists to remove inactive or invalid addresses, and engage subscribers with relevant and personalized content.
- Monitor Sender Reputation: Utilize tools to track and improve sender reputation by addressing issues like high bounce rates and spam complaints promptly.
- Optimize Email Content and Design: Create mobile-friendly, well-designed emails with compelling content that encourages engagement, reducing the likelihood of being marked as spam.
- Stay Informed About Industry Changes: Keep abreast of updates from email providers regarding authentication requirements and filtering algorithms to ensure compliance and adapt strategies accordingly.
By proactively addressing these areas, marketers can improve their email deliverability rates and ensure their messages reach their intended audience effectively.
Key Metrics to Monitor
Here is an expansion on the key components and factors influencing email deliverability:
| Metric | Goal/Impact | Why it Matters for Deliverability |
| Inbox Placement Rate (IPR) | Aim for |
The ultimate measure: percentage of emails landing in the main inbox. |
| Spam Complaint Rate | Keep below |
The most damaging signal to sender reputation. |
| Hard Bounce Rate | Keep below |
Signals list quality issues and poor list hygiene. |
| Open Rate | Varies by industry/list, but high is good. | A key positive engagement signal; proves the subject line is effective and the sender is trusted. |
| Click-Through Rate (CTR) | Varies by industry/list. | A strong positive engagement signal; proves content is relevant and valuable. |
| Unsubscribe Rate | Keep low, but it’s better than a spam complaint. | Indicates list fatigue or irrelevant content. |