Gmail 550 5.7.26
Blocked: unauthenticated or DMARC failure
Gmail 550 5.7.26 means: blocked: unauthenticated or DMARC failure. It is a permanent failure, so do not retry it unchanged. The message failed SPF and DKIM, failed an SPF hard fail, or failed the From domain's DMARC policy. Authenticate with SPF and DKIM aligned to the From domain.
Gmail’s exact wording
Quoted from Google Workspace Admin Help: Gmail SMTP errors and codes, checked 2026-11-05. Placeholders are Gmail’s own.
Reply text
This email has been blocked because the sender is unauthenticated. Gmail requires all senders to authenticate with either SPF or DKIM. Authentication results: DKIM = did not pass SPF [ domain-name ] with ip: [ ip-address ] = did not pass. For instructions on setting up authentication, go to Email sender guidelines.
Reply text
The (E)MAIL FROM domain [ domain-name ] has an SPF record with a hard fail policy (-all) but it fails to pass SPF checks with the ip: [ ip-address ]. To best protect our users from spam and phishing, the message has been blocked. For more information, go to Email sender guidelines.
Reply text
Unauthenticated email from domain-name is not accepted due to domain's DMARC policy. Contact the administrator of domain-name domain if this was legitimate email. To learn about the DMARC initiative, go to Control unauthenticated email from your domain.
| Who sends it | Gmail and Google Workspace |
|---|---|
| Basic code | 550: Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons) (RFC) |
| Enhanced code | 5.7.26: Multiple authentication checks failed |
| Permanent or temporary | Permanent (5xx) |
| Verifying the list prevents it | No |
In practice
Since February 2024, Gmail has required every sender to pass SPF or DKIM, and bulk senders to have both plus DMARC. 550 5.7.26 is the permanent block for three cases Google lists separately: mail that passes neither SPF nor DKIM, an SPF hard fail (-all) on the envelope domain, and a From domain whose DMARC policy rejects unauthenticated mail. The Authentication results line in the bounce tells you which check failed. Fix authentication first; resending the same message unchanged will be blocked again.
What the sender should do
The message failed SPF and DKIM, failed an SPF hard fail, or failed the From domain's DMARC policy. Authenticate with SPF and DKIM aligned to the From domain.
Would verifying the list have prevented Gmail 550 5.7.26?
No
This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
Common questions
- What does Gmail 550 5.7.26 mean?
- Gmail 550 5.7.26 means: blocked: unauthenticated or DMARC failure. It is a permanent failure, so do not retry it unchanged. The message failed SPF and DKIM, failed an SPF hard fail, or failed the From domain's DMARC policy. Authenticate with SPF and DKIM aligned to the From domain.
- Should I retry after Gmail 550 5.7.26?
- No. It is a permanent (5xx) failure, so the same message to the same address will fail again. Fix the cause first. The message failed SPF and DKIM, failed an SPF hard fail, or failed the From domain's DMARC policy. Authenticate with SPF and DKIM aligned to the From domain.
- Would verifying my list have prevented Gmail 550 5.7.26?
- No. This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.
The same code elsewhere
Sources
- Google Workspace Admin Help: Gmail SMTP errors and codes (checked 2026-11-05)
- IANA: SMTP Enhanced Status Codes registry (checked 2026-11-05)
- RFC 5321: Simple Mail Transfer Protocol, section 4.2.3 (reply codes) (checked 2026-11-05)
Registry and provider wording is quoted exactly; guidance is written by the SimpleVerifier Team.
SimpleVerifier Team · Last checked against the sources 2026-11-05