Hi list, Long time lurker here. Ran into an issue where one of my customers is sending mail with the sender- and header-from domain capitalized: foou...@example.tld. This seems to break DMARC checks on certain receivers.
The domain has all the bells and whistles, SPF, DKIM, DMARC... Everything is looking good, but (at least) the Proofpoint (UK) mailservers reject messages sent by this user stating "5.7.0 Local Policy Violation - DMARC Permerror". The sender domain DMARC record has 'p=none', for what it's worth. I've been playing around a bit and found out that the Proofpoint DMARC validator, as well as the one used at mail-tester.com fwiw, choke on the capitalization of the Return-Path / Envelope Sender address. Mail-tester.com states "The DMARC test failed but we didn't find any obvious reason why." The header from address doesn't matter. So long as the domain used in the envelope sender is capitalized it fails DMARC check. I always thought e-mail addresses weren't supposed to be case sensitive. Am i hitting a weird bug here? Have others seen this behaviour? Tests with my Exim MTA show it passing no matter what capitalization is used. My Exim is compiled against libopendmarc2 1.3.2. I'm currently rewriting the return path of all emails to lower case in hopes of working around this thing. Any insights appreciated! Regards, -Sndr. -- | denial, n.: not just a river in egypt. | 4096R/20CC6CD2 - 6D40 1A20 B9AA 87D4 84C7 FBD6 F3A9 9442 20CC 6CD2 _______________________________________________ mailop mailing list mailop@mailop.org https://list.mailop.org/listinfo/mailop
