It looks like GMX has upped their anti-spam measures, temp rejecting valid mails from GMX to GMX recipients delivered
through a forwarder at our site. DKIM is valid as the mail wasn't modified in transfer, SPF should be ok as we're
creating a SRS-wrapped SMTP MAIL FROM sender, so it shouldn't be a DMARC issue.
Still, GMX refuses to accept those mails. I've used their feedback form referenced in the error message
(https://postmaster.gmx.net/en/case?c=r0104) and got this reply:
Hello,
Thank you for your query.
We regret the delayed acceptance or temporary rejection of your e-mails.
This is due to the negative reputation of the surrounding network area.
Based on your DKIM domain(s), an automated reputation determination will be
carried out so that unhindered delivery to our system should be possible again.
Please be patient.
24 hours after the first blocked mail, there's no change. My understanding is that their rejection reason is pretty weak
and should be superceded by a whitelisting entry when it causes issues for legitimate mail.
Is there someone from GMX/IONOS who can check or explain this?
Cheers,
Hans-Martin
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