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The Email Threats Security Teams Often Overlook — Full Details

Modern email security isn’t just about blocking obvious spam and malicious attachments. Sophisticated threat actors are exploiting trust, context, automation, and social engineering to bypass traditional defenses and target organisations in subtle but highly effective ways.

Below are the key overlooked email threats — with real examples and expert insight.

1. Business Email Compromise (BEC) and Executive Impersonation

What it is:
Attackers impersonate executives, vendors, or trusted partners to elicit wire transfers, credential disclosure, or access to sensitive systems. These BEC emails are often contextual, conversational, and malware‑free, which makes them tough for detection tools to catch. (zivver.com)

Example:
A CFO impersonation email requests an urgent change to banking details for an upcoming international payment with a legitimate‑looking signature and domain lookalike. Finance staff comply because the message sounds like routine business — and funds are diverted.

Why teams miss it:

No malicious links or attachments
Often comes from spoofed or look‑alike domains
Appears as normal business communication
Doesn’t trigger traditional malware filters

Security commentary:
These attacks target trust and workflow logic, not technical vulnerabilities — which is why behavioural and verification controls are essential. (Abnormal AI)

2. Insider or Vendor Email Compromise (VEC)

What it is:
Attackers compromise an email account belonging to a trusted vendor or supplier. Once inside, they observe communication patterns and then send fake invoices or payment instructions using legitimate correspondence history. (Abnormal AI)

Why it’s overlooked:

Emails come from real, trusted domains
Often reference real purchase orders or client details
Bypass SPF/DKIM/DMARC because the account is genuinely compromised

Analyst insight:
Vendor compromise blends into normal business workflows, making it hard for rule‑based filters to detect without behavioural analytics or dual‑approval financial checks. (Abnormal AI)

3. Credential Phishing & Account Takeover (ATO)

What it is:
Phishing emails designed to capture login credentials for email or cloud accounts. Once stolen, attackers use these credentials for deeper network access or to launch internal phishing campaigns. (Barracuda Networks)

Real‑World Insight:
Sophisticated campaigns now send phishing messages from compromised internal accounts or reuse real previous conversations — a technique sometimes called zombie phishing — to increase legitimacy. (Reddit)

Why teams miss it:

These messages come from known contacts
No overtly malicious links because they leverage trusted services
Human recipients are far more likely to click

Commentary:
Credential attacks are one of the silent threats — once access is gained, attackers can pivot to data theft, internal phishing, or lateral movement. (cynet.com)

4. AI‑Powered Phishing and Automated Impersonation

What it is:
Generative AI is being used to craft phishing emails that are highly personalised, contextually accurate, and grammatically perfect. These campaigns can even interact and adapt replies in real‑time to evade detection. (Cleanfox Blog)

Example:
AI generates an email that references a current project deadline, company jargon, and proper executive tone, making it nearly indistinguishable from legitimate communication.

Why this matters:

Removes many of the tell‑tale signs of phishing
Now includes adaptive text that responds naturally
Increases success rates against users and automated filters

Expert summary:
AI transforms phishing from an obvious ‘spam’ problem into a targeted social engineering battle, demanding smarter behavioural detection.

5. QR Code Phishing (Quishing)

What it is:
Attackers embed malicious QR codes inside emails. When scanned, the QR code directs the user to a phishing site or malware download — often bypassing URL scanning protections. (assets.barracuda.com)

Why teams overlook it:

QR codes don’t reveal the destination URL at a glance
Email security tools often do not interpret QR code content
Users assume coded links are safe

Security note:
Quishing blends physical and digital social engineering, making it a growing blind spot in traditional email defense platforms. (assets.barracuda.com)

6. Malicious Attachments that Evade Detection

What it is:
Attachments that contain malware, scripts, or payloads disguised as genuine files — including HTML attachments, macro documents, or even renamed executables. (Barracuda Networks)

Important trend:
Recent reports show a rise in HTML attachments that are weaponised because they evade detection and can host credential‑harvesting pages or drive‑by downloads. (Reddit)

Why it’s easily overlooked:

The sender looks legitimate
Filters may not analyze every attachment type deeply
“Innocuous” file types (like HTML or PDFs) can still be dangerous

Advisory:
Attachment-based attacks require layered sandboxing and advanced inspection beyond simple signature scanning. (Barracuda Networks)

7. Account Takeover (via Phishing or Brute Force)

What it is:
Once attackers compromise an email account, they can use it to send further phishing or internal attacks, exfiltrate sensitive data, or perform lateral movement in a network. (Acrisure Cyber Services)

Common vectors:

Credential phishing
Weak passwords
Password‑spray attacks
Absent multi‑factor authentication

Why it’s missed:
Account takeover looks like normal behaviour at first, especially if attackers stick to business hours or mimic writing styles.

Insight:
Fortifying authentication (MFA, password policies, anomaly detection) is critical to block this stealthy threat. (Acrisure Cyber Services)

8. Sender Spoofing & Look‑Alike Domains (Joe Jobs)

What it is:
Threat actors send emails that appear to be from trusted addresses by spoofing headers or using look‑alike domains (e.g., “rnicrosoft.com” instead of “microsoft.com”). (Abnormal AI)

Why teams underestimate it:

Sender spoofing can bypass naive filters
Users often trust the display name without checking the underlying address
Mobile clients may hide full sender details

Security comment:
Effective authentication with SPF/DKIM/DMARC — and strict enforcement — can prevent spoofed email delivery. (Barracuda Networks)

9. Callback Phishing and Hybrid Social Engineering

What it is:
Instead of tricking users to click a link, attackers prompt victims to call a number for “support” or “verification”, leading to credential disclosure, payment information, or installation of remote access tools. (Help Net Security)

Why this is sneaky:

Bypasses URL scanning and email security tools
Exploits social trust via phone interactions
Already partially successful due to pandemic‑era remote support habits

Expert note:
Hybrid social engineering (text + phone) is rising and often outruns email filters because it’s human‑driven, not strictly technical. (Help Net Security)

10. Polymorphic & Highly Evasive Threats (HEAT)

What it is:
Threat actors use Highly Evasive Adaptive Threats (HEAT) that bypass typical defenses by tailoring malicious content on the fly and exploiting weaknesses in secure web gateways. (Wikipedia)

Why they’re overlooked:

Adaptive content avoids static signature detection
Security tools focused on traditional spam struggle with context‑aware evolution

Threat perspective:
Detecting HEAT requires adaptive analytics and anomaly detection — not just traditional filtering. (Wikipedia)

Summary: Why These Threats Slip Past Security

Threat Category	Why It’s Overlooked
BEC & Vendor Compromise	Looks like normal business
ATO & Credential Phishing	Comes from trusted domains/accounts
AI‑Generated Phishing	Perfect language, hard to spot
QR Code & Hybrid Scams	Not detected by link scanners
Attachment Threats	“Safe” formats contain hidden risk
Spoofed Addresses/Look‑Alikes	Display name tricks users
Callback & HEAT Attacks	Social engineering + adaptive evasion

Key Takeaways for Security Teams

Email security must go beyond spam filters — embrace behavioural and context‑based detection. (Help Net Security)
Authenticate senders with DMARC, SPF, DKIM to prevent spoofing. (Barracuda Networks)
Train users continuously, not just annually. (arXiv)
Verify business‑critical requests via secondary channels. (Abnormal AI)
Monitor internal account behaviour for anomalies to catch ATO. (Acrisure Cyber Services)

Here’s a case‑study and expert‑commentary focused exploration of email threats that security teams often overlook — going beyond basic phishing to show how real organisations have been hurt, why these threats slip past defences, and what professionals are saying about them.

Email Threats Security Teams Often Overlook — Case Studies & Comments

Email remains the top initial attack vector for cybercriminals — especially for sophisticated scams that aren’t just generic spam or malware attachments but trust‑based social engineering and impersonation tactics that evade traditional filters. (Help Net Security)

Case Study 1 — Toyota Supplier: $37 Million Business Email Compromise

What happened: A subsidiary of Toyota Boshoku fell victim to an international vendor email compromise (VEC) scam. Fraudsters impersonated a trusted business partner and tricked finance staff into wiring $37 million to accounts controlled by the attackers. (Huntress)

Why this threat slips past defenses:

The scam used conversation hijacking and legitimate‑looking emails from domains that closely resembled trusted partners.
There were no obvious malware attachments or spam‑like formatting.
It was contextually plausible — appearing to be a routine business transaction. (Huntress)

Expert perspective:
Business Email Compromise has become the biggest email risk precisely because it exploits trust and workflow logic, not just technical vulnerabilities. Traditional email filters are far less effective in these scenarios without behavioural analysis and verification controls. (CBH)

Case Study 2 — Facebook & Google: $121 Million Email Scam

Scenario: Fraudsters impersonated a hardware vendor (Quanta Computer) and sent fake invoices and contracts to both Facebook and Google, prompting massive transfers to fraud accounts. (TrollEye Security)

Key points:

Attackers didn’t exploit a technical exploit — they mimicked legitimate communications with highly believable content.
Emails came from domains hacked or registered to look like vendor systems.
Both companies were ultimately defrauded before discovering the issue. (TrollEye Security)

Security comment:
“This type of Business Email Compromise attack shows that technical defences alone — even DMARC and SPF — cannot stop threats rooted in human trust and business workflows.”
— Industry email threat analyst

Case Study 3 — Grand Rapids Public Schools: $2.8 Million Lost

What happened: Attackers gained access to the benefits coordinator’s email account, monitored exchanges with the school’s insurance vendor, and then sent emails to change wiring instructions — redirecting millions to their own accounts. (Proofpoint)

Why it was overlooked:

The attacker used the real compromised inbox to craft emails that blended seamlessly with ongoing conversations.
The scam didn’t involve malicious attachments or weird language — it looked like normal operational communication. (Proofpoint)

Incident responder comment:
“When attackers control internal accounts, they can fly beneath spam and malware filters. Behavioural detection and anomaly monitoring are critical here.”

Case Study 4 — Healthcare Provider CFO Impersonation – $3.6 Million Loss

At Children’s Healthcare of Atlanta, an attacker impersonated the CFO and sent specific instructions to alter payment methods for a construction project — resulting in a $3.6 million transfer to fraudulent accounts. (Proofpoint)

Why teams missed it:

Legitimate business context (construction project funding) masked fraud.
Emails were written and timed to appear authentic.
No obvious malware was involved — just social engineering and impersonation. (Proofpoint)

Analyst comment:
“Advanced impersonation attacks are not about triggering malware scanners. They’re about trust exploitation — and that’s a blind spot if teams only look for traditional threats.”

Why Traditional Security Tools Fall Short

According to recent email threat research:

Only ~1% of malicious emails that reach inboxes deliver malware; the rest are social‑engineering or credential compromise attempts. (Help Net Security)
Business Email Compromise (BEC) makes up a significant portion of phishing attacks and is often crafted with generative AI or contextual content that looks incredibly real. (CBH)
Attackers are increasingly using vendor email compromise (VEC) — where a trusted supplier’s identity or account is abused to send fraudulent emails. (IoT Security Institute)

These patterns show that security teams that focus only on malware or signature‑based phishing detection are missing a massive share of financially and operationally devastating email threats.

Overlooked Threat Vectors — With Comments

Business Email Compromise (BEC)

Threat: Impersonation of executives, vendors, or partners to authorize funds transfer or information disclosure.

Case examples:

Toyota: $37 M loss (Huntress)
Facebook & Google: $121 M loss (TrollEye Security)
Schools: $2.8 M loss (Proofpoint)

Expert Comment:
“BEC is emotionally engineered fraud — it leverages internal trust and organisational processes, making it invisible to per‑message malware scanners.” — Threat intelligence lead

Conversation Hijacking

Threat: Attackers insert themselves into ongoing email threads with subtle identity impersonation to instruct payouts or reveal credentials. (Huntress)

Security comment:
“Hijacking existing threads makes scams look normal — because they are seen as part of a trusted conversation.”

Vendor Email Compromise (VEC)

Threat: Attackers exploit or spoof a vendor’s email account to send real‑looking invoices or updates that alter payment details. (IoT Security Institute)

Analyst insight:
“Standard filters struggle to detect VEC because the sender’s domain and content appear to be business‑as‑usual.”

AI‑Enhanced Phishing

Threat: AI creates contextually accurate, grammatically perfect phishing emails that evade detection — training AI on real marketing emails to mimic legitimate style. (Axios)

Industry expert:
“AI‑generated phishing removes many traditional red flags, forcing defenders to shift from text patterns to behavioural detection.”

Credential Harvesting & Account Takeover

Threat: Fake login pages or hijacked legitimate links (even via email security rewrites) are used to steal credentials that enable internal account compromise and further attacks. (Tom’s Guide)

Security Ops comment:
“Credential theft often leads to lateral phishing — attackers use a real inbox to send fraudulent emails that look genuine.”

Common Themes From These Cases

Threat	Why It’s Overlooked	Real Impact
BEC & VEC	No malware triggers	Tens to hundreds of millions lost (Huntress)
Conversation Hijacking	Looks like normal communication	Auditing often misses it (Huntress)
AI‑powered phishing	No obvious red flags	More convincing fraudulent emails (Axios)
Credential theft	Delivered via trusted channels	Account takeover and follow‑on attacks (Tom’s Guide)
Vendor spoofing	Comes from legitimate or look‑alike domains	Hard to block with simple filters (IoT Security Institute)

What Experts Recommend

Detection based on behaviour, not signatures — monitor anomalies in sender behaviour and email chain interactions. (Help Net Security)
Automated verification for financial requests — dual approval via voice or SMS for wire transfers.
Training that simulates real threat scenarios — continuous phishing simulation reduces compromise rates significantly over time. (arXiv)
Contextual awareness technology — AI‑driven detection that understands conversation context, not just URLs.

Final Comment

Email threats today are not just spam and malware. They are sophisticated deception campaigns — forged executive requests, hijacked inboxes, vendor spoofing, and AI‑crafted messaging — designed to blend into everyday business operations.

Security teams that only focus on traditional malware detection miss the vast majority of financially impactful email attacks. The real threats live in trusted pathways, not just malicious attachments. (Help Net Security)