THIS IS INTENDED TO POSTMASTER OF HISPEED.CH
I sent a message through an email forwarding service that redirects an email to a final address …@hispeed.ch and following error was returned by the mx of UPC:
554 5.2.0 MXIN603 DMARC validation failed. ;id=yVD2nletwsewfyVD2nuzPb;sid=yVD2nletwsewf;mta=vie01a-pemc-pmxin-pe13;dt=2022-06-07T11:09:09+02:00;
The origin sender (domain) has SPF and DKIM configured correctly and set DMARC policy to reject. Since SPF breaks on mail forwarding, only DKIM check passes. DMARC requires either one of DKIM or SPF to pass and not both. My observation so far was that the MX of hispeed.ch requires both (SPF and DKIM) to pass. Instead, the correct behavior for DMARC pass would be either a DKIM pass or a SPF pass (see RFC https://datatracker.ietf.org/doc/html/rfc7489).
I hope the postmaster of hispeed.ch sees this post, because I was not successful to reach out to the postmaster via contact form.