Are they using Windows Mail to send mail through your service via message submission?
Adding a message-id header is a SHOULD in that case: https://datatracker.ietf.org/doc/html/rfc6409#page-14 If you're just forwarding, then yes, it's unfortunate. Brandon On Mon, Jul 18, 2022 at 4:24 PM Robert L Mathews via mailop < [email protected]> wrote: > On 7/13/22 12:31 AM, Philip Paeps via mailop wrote: > > In the past couple of days, I'm seeing an uptick in rejects from Gmail > > as follows: > > > > >Our system has detected that this message is not RFC 5322 compliant. > > Similar to this, some our customers complained that messages sent to > Gmail have been bouncing since June 15 with: > > 550-5.7.1 [ip_redacted] Messages missing a valid messageId header are not > 550 5.7.1 accepted. > > The messages indeed do not have a "Message-ID" header; they're being > sent from the Windows 10 built-in "Mail" app. > > I'm a little surprised that the Windows Mail app doesn't include a > Message-ID, but > <https://datatracker.ietf.org/doc/html/rfc5322#section-3.6.4> says it's > only a SHOULD, not a MUST. > > Anyone else seeing the same thing? Now I'm in the position of having to > either start adding missing Message-ID headers, which people online > recommend against because it potentially breaks DKIM, or telling people > Windows Mail no longer works to send to Gmail. Neither is ideal. > > -- > Robert L Mathews > _______________________________________________ > mailop mailing list > [email protected] > https://list.mailop.org/listinfo/mailop >
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