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Problems with rspamd, DKIM and a body getting altered after dkim signing because of changed content-transfer-encoding

Hi to all of you,

since weeks I'm struggling with this problem, not being able to solve
it on my own and I think the last possibility of getting help is to
ask you, the experts right here.
I set up a mailserver with the help of a howto I found on the net.
Mainly everything is okay, mails are received and sending is also
possible. Spam is getting sorted out and DKIM, SPF and DMARC is
working on the domains I switched to that new mailserver.

A few weeks ago I figured out that there is a problem when a
conversation is going on via mail, at some point the postfix changes
the content-transfer-encoding from 7bit to quoted-printable.
This makes sense, the MTA postfix is doing what it is expected to.
I've read about line-lengths, 8bitmime, utf8 and so on. But this
behaviour is breaking DKIM signing, as signing with rspamd is done
before the encoding conversion.

So I hope there is a possibility to get this problem solved with your help.
Please forgive me that at this point I did not post any details as I
am waiting for you telling me what configs, logs, snippets, headers
and so on you need to have in order to be able to help.
What I know is that rspamd is called via the milter functionality of
postfix. But I didn't find any ressources on the net on how to change
the order, so that rspamd dkim signing comes last.
This seems to be important in the master.cf as that must be the point
where the smtps-session is controlled. But I can't see anything where
it calls the milter, so that is why I have no clue where to begin
searching.

So any help is greatly appreciated.

Best regards,
Michael

Comments

Re: Problems with rspamd, DKIM and a body getting altered after

By Wietse Venema at 03/12/2019 - 20:06

Michael Ludwig:
No, it doesn't. Postfix may convert 8bit mail into 7bit quoted-printable,
depending on whether disable_mime_output_conversion is yes or no,
and whether a down-stream SMTP receiver anounces 8BITMIME support.

Postfix does not convert 7bit mail into quoted-printable. That is
how it has worked since 2002.

Please solve the right problem.

Wietse