On 6/5/23 07:06, Peter Münster wrote:
Hi,
I'm using mailman 3.3.8.
Some messages with attachments from Google users get rejected by spam filters because of invalid DKIM signatures.
It seems, that mailman alters some lines in the body. Here an example:
Original message:
--8<---------------cut here---------------start------------->8--- Lines: 2031
--000000000000f846c505fc494b7a-- --000000000000f846c705fc494b7c Content-Type: application/pdf; [...] Content-Disposition: attachment; [...] --8<---------------cut here---------------end--------------->8---
Altered message:
--8<---------------cut here---------------start------------->8--- Lines: 2032
--000000000000f846c505fc494b7a--
--000000000000f846c705fc494b7c Content-Type: application/pdf; [...] Content-Disposition: attachment; [...] --8<---------------cut here---------------end--------------->8---
An empty line is added, and the spaces after the semicolons are removed.
Perhaps related to https://gitlab.com/mailman/mailman/-/issues/1079.
What could I do please, to prevent such modifications of the body?
Changes like those above are due to Python's stdlib email module. Short of actually modifying the email module, there's nothing you can do to prevent them.
Instead, you should be DKIM signing your outgoing mail and perhaps applying Mailman's DMARC mitigations if DMARC is an issue.
If you are DKIM signing your outgoing mail and mail is being rejected
because of prior invalid signatures, you can remove those by adding
remove_dkim_headers: yes to the [mta] section of mailman.cfg. Also,
ARC signing
<https://docs.mailman3.org/projects/mailman/en/latest/src/mailman/handlers/docs/arc_sign.html>
may help.
-- Mark Sapiro <mark@msapiro.net> The highway is for gamblers, San Francisco Bay Area, California better use your sense - B. Dylan