Hello,
Steve Atkins via mailop wrote on 21.10.24 at 18:04:
Chatting with Florian off list it seems likely that the Postfix smarthost is
accepting Content-Transfer-Encoding: 8bit messages, DKIM signing them, only
then discovering that the recipient MX doesn’t offer 8BITMIME. It rewrites the
body using quoted-printable encoding, breaking the signature in the process.
So an MUA sending 8bit mail to a non-8BITMIME recipient may cause the signature
to break. Setting force_mime_input_conversion to reencode all 8bit mail on
submission looks like a fix, for a signing outbound server anyway.
thanks so much for your support indeed!
What puzles me a lot is where the problem comes from. I consider my
setup pretty much standard here - I connect to my MX, which sends out
the message that it routes through rspamd, which takes care of DKIM
signing. No other modification of the mail takes place, no other filter,
milter or proxy is in between, no other smarthost, I directly send the mail.
Postfix has SMTPUTF8 disabled because of Dovecot-LMTP, that is the
unique setting on encoding I configured.
That's a setup that's probably in wide use out there. Mail clients in
use are Thunderbird and Roundcube, also that is pretty much standard.
Right now I don't see anything weird in my configuration, but probably I
miss something...
Thanks everyone for your help so far, I really appreciate it!
Florian
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