https://community.mimecast.com/s/article/email-security-cloud-gateway-mimecast-smtp-error-codes
It's in there. Search for "DKIM sender invalid". -Mark Alley On Thu, Oct 17, 2024, 6:47 AM Florian Effenberger via mailop < mailop@mailop.org> wrote: > Hello, > > I've recently ran into an issue with delivering mails to a > Mimecast-hosted domain. > > I do not have delivery issues to any other MX, there are no blocklist > entries, and SPF, DKIM and DMARC are working as expected. I've just > confirmed this again via mail-tester.com and dmarctester.com. > > A domain one of my users has been sending to for the past 25 years just > earlier this week switched to Mimecast, and since then the majority of > mails get blocked with "550 DKIM Sender Invalid - envelope rejected", > other mails make it through. So far, I see no pattern what might trigger > the 550. Senders and recipient differ and the choice of mail client > seems to make no difference either. As all of the outgoing mails use the > same MX, it's unlikely DKIM signing works on some and not on others > (plus then I would also see rejections from other sites). > > For now, I assume it's a problem on the recipient's end, perhaps some > misconfiguration. That particular error message is not listed on > https://community.mimecast.com/s/sender-feedback either. > > Anyone has insight how to nail down that issue? > > Thanks > Florian > _______________________________________________ > mailop mailing list > mailop@mailop.org > https://list.mailop.org/listinfo/mailop >
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