On 2025-10-29 09:57:53, flagg--- via mailop wrote: > Hi all, > > if you're struggling with Gmail inbox placement despite clean headers > and good reputation, your ESP might be sabotaging your messages without > your knowledge. SendGrid's SMTP relay violates RFC 2047 and RFC 2369 by > MIME-encoding the List-Unsubscribe header as soon as its value exceeds > 77 bytes. This breaks unsubscribe links in Gmail and Outlook. The issue > has been confirmed internally but remains unresolved. SendGrid sends > over 100 billion emails per month - this is a massive standards > compliance failure with real-world consequences for deliverability and > compliance.
SendGrid has confirmed on this list before that they parse 4xx responses (an RFC violation) and sometimes decide not to retry those messages. In the past, they also threw away messages where the connection to the recipient's MX failed -- a separate RFC violation. The latter is probably still ongoing, but I can't say with certainty now that Github has (thank god) stopped using sgmail.github.com for notifications. They do what is cost-effective for their clientele, who are of the sort that send 100 billion messages a month with broken unsubscribe links. If you aren't one of those, there's probably a better ESP. _______________________________________________ mailop mailing list [email protected] https://list.mailop.org/listinfo/mailop
