Spam filter · 5.x.x permanent failure
Every SMTP 554 response on record from Mimecast, with the verbatim text, the enhanced status code, a severity rating and a plain-English fix.
The transaction failed with no more specific reason offered. In practice the receiver is saying the message is unwanted: a spam verdict, a blocklisted IP, or a policy rejection. The accompanying text is where the detail is.
smtp;554 Email rejected due to security policies - https://community.mimecast.com/docs/DOC-1369#554 [#]
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.
Postmaster & documentation
The transaction failed with no more specific reason offered. In practice the receiver is saying the message is unwanted: a spam verdict, a blocklisted IP, or a policy rejection. The accompanying text is where the detail is. 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.
