Spam filter · 5.x.x permanent failure
Every SMTP 550 response on record from FireEye, 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 5.7.26 <[email protected]>: ETP205 DMARC Failure for domain
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.
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 FireEye, 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.
