Email provider · 5.x.x permanent failure
Every SMTP 550 response on record from Google (gmail.com, googlemail.com), 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 5.1.1 The email account that you tried to reach does not exist. Please try double-checking the recipient's email address for typos or unnecessary spaces. Learn more at https://support.google.com/mail/?p=NoSuchUser - gsmtp
The address does not exist, or is no longer active, at this provider. Remove it from your list and check for a typo in the local part or the domain.
Provider documentation
smtp;550 5.2.1 The email account that you tried to reach is disabled. Learn more at https://support.google.com/mail/?p=DisabledUser - gsmtp
The receiver refused the message for good and points at a mailbox problem (missing, disabled, or full) (enhanced status 5.2.1). Use the wording above to pin down the exact fix.
Provider documentation
smtp;550 5.2.1 The user you are trying to contact is receiving mail at a rate that prevents additional messages from being delivered. For more information, please visit https://support.google.com/mail/?p=ReceivingRatePerm - gsmtp
You are sending to this receiver faster than it will accept from your IP or domain, and it has stopped taking the message. Cut the send rate, spread volume over a longer window, and requeue.
smtp;550 5.7.1 [x.xx.xx.xx] Our system has detected that this message is likely suspicious due to the very low reputation of the sending domain. To best protect our users from spam, the message has been blocked. Please visit https://support.google.com/mail/answer/188131 for more information. - gsmtp
The receiver's spam filter scored the message above its rejection threshold. Review the content and links, build sending reputation gradually, and only mail people who asked to hear from you.
Provider documentation
smtp;550 5.7.1 [x.xx.xx.xx] Our system has detected that this message is likely unsolicited mail. To reduce the amount of spam sent to Gmail, this message has been blocked. Please visit https://support.google.com/mail/?p=UnsolicitedMessageError for more information. - gsmtp
The receiver's spam filter scored the message above its rejection threshold. Review the content and links, build sending reputation gradually, and only mail people who asked to hear from you.
Provider documentation
smtp;550 5.7.1 Unauthenticated email from example.com is not accepted due to domain's DMARC policy. Please contact the administrator of example.com domain if this was a legitimate mail. Please visit https://support.google.com/mail/answer/2451690 to learn about the DMARC initiative. - gsmtp
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
smtp;550 5.7.1 [x.xx.xx.xx 14] Messages missing a valid address in From: header, or having no From: header, are not accepted. - gsmtp
The receiver refused the message for good and points at a policy or security problem (enhanced status 5.7.1-4). Use the wording above to pin down the exact fix.
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 Google, 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 Google's postmaster documentation.
