> Am 15.10.2026 um 12:54 schrieb Cor Bosman via mailop <[email protected]>: > > I think it’s relatively new, we only started seeing this recently. I think > Microsoft/Outlook changed something in the way or order they process their > incoming mail.
I think it started about half a year ago. > We allow users to add forwarding addresses on their mail, letting postfix > handle the actual forwarding through our dedicated forwarding servers. We use > SRS, but the body/DKIM stays intact. So normally DMARC still validates. And > for most mail that still works fine. From my observations I can say it does not matter if it is forwarded mail or originating from our own servers. > Only when the sender has duplicate headers AND signs that header with DKIM > Microsoft now refuses them. That is the reason: I suspect that Microsoft removes duplicate headers _before_ doing the DKIM check and that breaks the DKIM signature. Regards, Bernhard
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