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Comcast SMTP 554 Errors: Every Bounce Response Explained

Every SMTP 554 response on record from Comcast (comcast.net), 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.

Provider
Comcast
Code
554 (5xx)
Responses
2
Highest severity
Low

Comcast SMTP 554 responses

Status 1Low severity#
host xx.comcast.net [x.xx.xx.xx] SMTP error from remote mail server after initial connection: 554 xx.comcast.net comcast x.xx.xx.xx Comcast requires that all mail servers must have a PTR record with a valid Reverse DNS entry. Currently your mail server does not fill that requirement. For more information, refer to: http://postmaster.comcast.net/smtp-error-codes.php#554

The receiver could not match your sending IP to a valid PTR (reverse DNS) record, or your HELO name does not resolve. Set forward-confirmed reverse DNS for every sending IP.

Provider documentation

Status 2Low severity#
554 xx.comcast.net comcast x.xx.xx.xx Comcast block for spam. Please see http://postmaster.comcast.net/smtp-error-codes.php#BL000000

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

Postmaster & documentation

Comcast SMTP 554 questions

›What does an SMTP 554 error from Comcast mean?

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 Comcast, it is a permanent rejection, and the specific reason is in the enhanced status code and message text of each response below.

›How do I stop Comcast from returning SMTP 554?

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 Comcast's postmaster documentation.

All SMTP 554 responsesAll Comcast error codes

Other error codes seen from Comcast