550 5.7.26: unauthenticated sender, blocked
Gmail rejected the message because it passed neither SPF nor DKIM, and Gmail requires every sender to pass at least one.
- Gmail
- Provider
- Permanent (5xx)
- Class
- Sources checked
- Author
At a glance
- Code
- 550 5.7.26
- Provider
- Gmail and Google Workspace
- Temporary or permanent
- PermanentRefused for good: the message comes back to the sender, and resending it gets the same answer.
- Who has to act
- The sender. The fix is on the sending side: your domain, your server or your list.
- What the server says
550 5.7.26 This email has been blocked because the sender is unauthenticated.
What it means
Since February 2024 every sender to Gmail has had to authenticate with SPF or DKIM. This message passed neither, so it was rejected. The reply lists what Gmail saw: DKIM did not pass, and SPF for the envelope domain and the sending IP did not pass. Google's sender guidelines warn that messages without this authentication might be marked as spam or rejected with a 5.7.26 error. The temporary form is 421 4.7.26, and our blog has a step-by-step guide to this one.
Common causes
- The sending server or service is not listed in the envelope domain's SPF record.
- DKIM signing is not turned on, or the selector record is missing from DNS.
- Forwarding broke SPF and there was no valid DKIM signature to fall back on.
How to fix it
- 01Read the authentication results in the bounce to see which domain and IP Gmail checked.
- 02Add every service that sends for you to your SPF record.
- 03Turn on DKIM signing at each sending service and publish its selector record.
- 04Send a test to a Gmail address and confirm that SPF or DKIM shows pass, then resend.
Sources
What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.
- Gmail SMTP errors and codes (Google Workspace Admin Help)knowledge.workspace.google.com
- Email sender guidelines (Gmail Help)support.google.com
Related codes
- 421 4.7.26Unauthenticated mail, rate limited.Gmail is slowing mail from you because this message passed neither SPF nor DKIM, and Gmail requires every sender to pass at least one.
- 550 5.7.26Rejected under the sender's DMARC policy.Gmail rejected the message because it failed DMARC, and the From domain's DMARC policy tells receivers to refuse mail that fails.
- 550Mailbox unavailable.The receiving server permanently refused the message for this recipient: the mailbox does not exist, cannot be reached, or the server rejected the message by policy.
- 550 5.7.26Multiple authentication checks failed.The message failed more than one authentication check, for example SPF and DKIM, and the receiving server's policy rejects it.
Further reading
All 108 Gmail codesEvery code in the wikiPaste your own bounce