Why are some legitimate emails being blocked?

Our email security system, Mimecast, helps protect you from unwanted and malicious emails. Sometimes, however, it might block emails you want to receive. Here are some common reasons why:

SPF (Sender Policy Framework): An email authentication method that detects forging sender addresses. Learn more about SPF
DKIM (DomainKeys Identified Mail): An email authentication method designed to detect forged sender addresses. Learn more about DKIM
DMARC (Domain-based Message Authentication, Reporting, and Conformance): An email authentication protocol that builds on SPF and DKIM. Learn more about DMARC

Unusual Email Headers: Mimecast carefully checks email headers. If there’s a discrepancy, such as a mismatch between the sending domain and the actual server, the email might be flagged.
Tracking Elements in Emails: Marketing emails often include tracking pixels or links to see if you’ve opened or clicked. If the tracking domain isn’t recognized as safe, these emails can be marked as suspicious.
Sender’s Reputation or IP Address: If the sender’s internet address (IP) has a poor reputation or isn’t on an approved list, Mimecast might block the email, even if it’s from someone you know.
Accidental Blocks: Occasionally, a sender’s address or domain might be unintentionally added to a blocked list, which can override your personal settings.
Third-Party Senders: If an email is sent on behalf of another domain (like from a CRM system or newsletter service), it could be blocked if the third party isn’t properly authorized in the sender’s DNS records.

Even when you try to “train” your inbox to recognize certain emails, Mimecast might still hold or reject them until you’ve explicitly “trusted” the sender.