Spam filter · 5.x.x permanent failure
Every SMTP 550 response on record from Mimecast, with the verbatim text, the enhanced status code, a severity rating and a plain-English fix.
The mailbox is unavailable and the message is rejected for good. This is the catch-all permanent failure, covering everything from an unknown address to an authentication failure to a reputation block, so the wording after the number is what actually tells you the reason.
smtp;550 Administrative prohibition - envelope blocked - https://community.mimecast.com/docs/DOC-1369#550 [#]
The receiver rejected the message under a policy rule rather than a content or reputation score. This is usually set by the recipient's mail admin, so ask the recipient to allowlist your sending address or domain.
smtp;550 Rejected by header based Anti-Spoofing policy: [email protected] - https://community.mimecast.com/docs/DOC-1369#550 [#]
The receiver rejected the message under a policy rule rather than a content or reputation score. This is usually set by the recipient's mail admin, so ask the recipient to allowlist your sending address or domain.
Provider documentation
smtp;550 Rejected by header based manually Blocked Senders: [email protected] - https://community.mimecast.com/docs/DOC-1369#550 [#]
The receiver rejected the message under a policy rule rather than a content or reputation score. This is usually set by the recipient's mail admin, so ask the recipient to allowlist your sending address or domain.
smtp;550 Envelope blocked - User Entry - https://community.mimecast.com/docs/DOC-1369#550 [#]
The receiver refused this message outright and will not accept an unchanged retry. The wording above is the only clue to what needs to change, most often the address, authentication, or sending reputation.
Provider documentation
smtp;550 DMARC Sender Invalid - envelope rejected - https://community.mimecast.com/docs/DOC-1369#550 [#]
The message did not pass the sending domain's DMARC policy, so the receiver rejected it. Sign the mail with DKIM for your From domain, or align SPF through a custom Return-Path, then send again.
Provider documentation
Postmaster & documentation
The mailbox is unavailable and the message is rejected for good. This is the catch-all permanent failure, covering everything from an unknown address to an authentication failure to a reputation block, so the wording after the number is what actually tells you the reason. At Mimecast, it is a permanent rejection, and the specific reason is in the enhanced status code and message text of each response below.
Match your bounce text to one of the responses below and follow its guidance. Recipient-side wording means fix the address. Authentication or reputation wording (SPF, DKIM, DMARC, blocklist) means fix your sending setup, and check Mimecast's postmaster documentation.
