Detection Method: Header analysis

Header analysis inspects the metadata in message headers to find suspicious patterns, anomalies, or inconsistencies that could indicate phishing, spoofing, or other types of malicious activity. It looks at various header fields like routing information, authentication results, and sender verification data to help spot potential threats.
This includes sender authentication headers like SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance) results to verify the sender's legitimacy. It also checks how the email traveled through mail servers, looking for any unusual routing that might suggest tampering.
Header analysis can detect:
  • Email spoofing, where attackers forge the sender’s address to appear legitimate
  • Mismatched or inconsistent sender details
  • Suspicious return paths that don’t match the expected sender
  • Unusual routing patterns that stand out from normal email flow
  • Authentication failures that signal potential impersonation attempts
For example, attackers might try to forge email headers to make phishing emails appear as if they’re coming from a trusted source like your bank or your company’s internal email. Header analysis helps you catch these attempts by identifying mismatches between the displayed sender and the actual sending server.
Rule Name & Severity
Last Updated
Author
Types, Tactics & Capabilities
Headers: Reserved domain in Message-ID
3h ago
Oct 26th, 2026
Sublime Security
Brand impersonation: QuickBooks
3h ago
Oct 26th, 2026
Sublime Security
Brand impersonation: Meta and subsidiaries
3h ago
Oct 26th, 2026
Sublime Security
Link: Multistage landing - Abused Adobe Acrobat hosted PDF
3h ago
Oct 26th, 2026
Sublime Security
Link: Romance/Sexual Language With Suspicious Link
4h ago
Oct 26th, 2026
Sublime Security
Brand impersonation: American Express (AMEX)
4h ago
Oct 26th, 2026
Sublime Security
Brand impersonation: Amazon
4h ago
Oct 26th, 2026
Sublime Security
Brand impersonation: Federal court system
4h ago
Oct 26th, 2026
Sublime Security
Observed IOC: Mail transiting OFAC-sanctioned bulletproof host Aeza Group
8h ago
Oct 26th, 2026
Sublime Security
Spamhaus: Mail transiting an ASN-DROP listed network
8h ago
Oct 26th, 2026
Sublime Security
Observed IOC: Malicious sender email addresses
8h ago
Oct 26th, 2026
Sublime Security
Spamhaus: Mail transiting a DROP listed network
8h ago
Oct 26th, 2026
Sublime Security
Credential phishing: Financial lure via ActiveCampaign infrastructure
4d ago
Oct 23rd, 2026
Sublime Security
Attachment: EML file with HTML attachment (unsolicited)
4d ago
Oct 23rd, 2026
Sublime Security
Brand impersonation: Dropbox
4d ago
Oct 23rd, 2026
Sublime Security
Brand impersonation: Google Workspace alert notification
4d ago
Oct 23rd, 2026
Sublime Security
Brand impersonation: Bluehost
4d ago
Oct 23rd, 2026
Sublime Security
Observed IOC: Malicious sender root domains
4d ago
Oct 23rd, 2026
Sublime Security
BEC/Fraud: Fake investment outreach from suspicious TLD
5d ago
Oct 22nd, 2026
Sublime Security
Credential phishing: Suspicious e-sign agreement document notification
5d ago
Oct 22nd, 2026
Sublime Security