Le vendredi 23 janvier 2026, 10:24:41 heure normale d’Europe centrale Florian Effenberger via mailop a écrit : > Hello, > > some while ago, this list greatly helped me out with an issue in > delivering to Mimecast, as some e-mails were claimed to have a broken > DKIM signature. > > After quite some research thanks to your support, we've discovered the > problem is the missing 8BITMIME support on their end. > > When the Content-Encoding was 8bit, it got bounced by Mimecast, and also > flagged as erroneus by aboutmy.email (which has 8BITMIME disabled as > well, so I could finally reproduce the problem). When I switched to > Quote-Printable, the mail passed just fine. > > For Postfix, a workaround (which I didn't try yet) seems to enable > force_mime_input_conversion in newer versions. > > These days, a friend of mine had a comparable issue. While I think it's > not a general Mimecast problem, but related to the recipient's specific > configuration, I want to share it here in case anyone else faces this issue. > > For them, the trigger was a special character (Umlaut) in the signature. > They fixed it client-side with > > mailnews.send_plaintext_flowed: false > mail.strictly_mime: true > > I didn't do further research yet about the side effects of this, but > maybe it helps others affected by this. > > Have a nice weekend, > Florian
Thank you so much! We have, at work, some problems with Microsoft saying that some e-mails have a broken DKIM signature. I confirmed that our mails have the DKIM problem with aboutmy.email when having an Umlaut in the FROM gecos. I upgraded the postfix of my mail servers to postfix >3.9 to have force_mime_input_conversion (thanks to Debian backports, I have been able to install postfix >3.9 on Bookworm), I added this setting to postfix and voilà, aboutmy.email is not complaining anymore. I really, really hope it will fix the problem with Microsoft. -- Luc https://fiat-tux.fr https://luc.frama.io Internet n'est pas compliqué, Internet est ce que vous en faites. _______________________________________________ mailop mailing list [email protected] https://list.mailop.org/listinfo/mailop
