1. Permanent codes

All three codes above are temporary messages. 
Google is only rate limiting messages that failed authentication checks, 
rather than outright rejecting them (for now) the messages should get delivered at a later time 
with no need for any changes to the messages. 


However, in the long term, authentication issues will still have to be addressed to meet the new requirements. 
If you’re not complying with the new authentication requirements when sending to Gmail inboxes, 
you might have received SMTP error message 550, 5.7.26:

550, "5.7.26", "This message does not have authentication information or fails to pass authentication checks (SPF or DKIM). To best protect our users from spam, the message has been blocked. 
Please visit Prevent mail to Gmail users from being blocked or sent to spam for more information."

This is a new error response related to the Gmail email sender requirements, joining two others that previously existed that start with “550-5.7.26”.

550, "5.7.26", "Unauthenticated email from domain-name is not accepted due to domain's DMARC policy. Please contact the administrator of domain-name domain. If this was a legitimate mail please visit Control unauthenticated mail from your domain to learn about the DMARC initiative. If the messages are valid and aren't spam, contact the administrator of the receiving mail server to determine why your outgoing messages don't pass authentication checks."

The above response will be received when mail sent using a domain with a DMARC policy of

• “p=reject” fails DMARC authentication.

550, "5.7.26", "This message fails to pass SPF checks for an SPF record with a hard fail policy (-all). To best protect our users from spam and phishing, the message has been blocked. Please visit Prevent mail to Gmail users from being blocked or sent to spam for more information."

The above response will be received when mail sent using a Return-Path (or bounce) domain that has an SPF record ending “-all” fails SPF authentication checks.

Only the first of these three indicates that the email message did not comply with the new email authentication requirements that Google has in place; the other two are rejections made at the request of the domain owner based on policies expressed in the domain owner’s DMARC or SPF record. That said, all of these error responses beginning with 550 are permanent errors, meaning that the message will not be accepted.

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