Gmail sender authentication rejection

Fix Gmail 550 5.7.27 SPF authentication failed

Gmail reports this when the message's SPF authentication did not meet its requirements. To diagnose it safely, evaluate the supplied sending IP against the SPF policy at the actual envelope MAIL FROM domain—not just the visible From domain or a website hostname.

Problem description

Gmail rejects mail from your domain with the following error message:

Gmail rejected: 550 5.7.27 SPF authentication failed.

Evaluate the sending SPF path

You need three inputs: the Gmail rejection excerpt, the sending IP, and the envelope MAIL FROM domain. MailFixIt does not calculate a message-level SPF result when any one of these is missing.

How to interpret the result

Pass: the supported SPF path authorizes the supplied IP at the current MAIL FROM policy. Review the fresh message and other delivery factors before concluding Gmail will accept every message.
Fail or softfail: the current evaluated policy did not authorize that IP with a pass result. Confirm the sender, then repair the correct SPF record or provider configuration.
Unknown: an unsupported SPF construct or temporary DNS result prevented a safe verdict. This is not a failed SPF result.

Safe repair sequence

Verify that the IP belongs to a service intended to send for the MAIL FROM domain.
Check whether the MAIL FROM domain is a subdomain with its own SPF record. Do not assume it inherits the parent policy.
Preserve the single current SPF record and every legitimate sender before changing it.
Use the sender provider's current authorization value; do not copy a generic include from an unrelated account.
Send a new test message after DNS updates and inspect its Authentication-Results.

What this does not check

SPF path evaluation does not prove DKIM signing, DMARC alignment, inbox placement, IP reputation or all recipient-specific policies. It only evaluates the supported public-DNS SPF path for the supplied identity and IP.

Reference: RFC 7208 SPF.