Spam filter / gateway
Mimecast SMTP Error Codes and Rejection Messages
Mimecast is a corporate mail security service. Inbound mail routes through Mimecast servers before the recipient's, and the recipient controls policy levels and allowlist overrides.
- Codes on record
- 3
- Responses
- 9
Postmaster & documentation
SMTP 4513 responses
A temporary problem. The sending server keeps retrying for a while, and delivery often recovers on its own once the underlying issue clears. See SMTP 451 across every provider
SMTP 5505 responses
smtp;550 Administrative prohibition - envelope blocked - https://community.mimecast.com/docs/DOC-1369#550 [#]
smtp;550 Rejected by header based Anti-Spoofing policy: [email protected] - https://community.mimecast.com/docs/DOC-1369#550 [#]
smtp;550 Rejected by header based manually Blocked Senders: [email protected] - https://community.mimecast.com/docs/DOC-1369#550 [#]
smtp;550 Envelope blocked - User Entry - https://community.mimecast.com/docs/DOC-1369#550 [#]
A hard failure. The receiving server has refused the message for good and will not accept an unchanged retry without a change on the sending side. See SMTP 550 across every provider
SMTP 5541 response
A hard failure. The receiving server has refused the message for good and will not accept an unchanged retry without a change on the sending side. See SMTP 554 across every provider
Mimecast bounce questions
›Why is Mimecast bouncing my email?
Mimecast is a corporate mail security service. Inbound mail routes through Mimecast servers before the recipient's, and the recipient controls policy levels and allowlist overrides. Match the exact wording of your bounce to one of the 9 responses on this page to find the specific reason and fix.
›How do I get past the Mimecast spam filter?
Authenticate with SPF, DKIM and DMARC, keep your sending IP and domain reputation clean, mail only engaged recipients, and honour unsubscribes. Mimecast also publishes postmaster guidance, linked on this page.
