Just if anyone has similar problems:
I followed
https://www.cubewerk.de/2017/12/04/spf-und-dkim-mit-univention-ucs-server/
and especialle the work from
https://kofler.info/dkim-konfiguration-fuer-postfix/
In my configuration (kopano with activated amavis) every outgoint email was signed twice. I solved this by following:
I just added an additional line
-o smtpd_milters=
in
/etc/univention/templates/files/etc/postfix/master.cf.d/30_antivir
The relevant part now looks like:
127.0.0.1:10025 inet n - n - - smtpd
-o content_filter=
-o local_recipient_maps=
-o relay_recipient_maps=
-o smtpd_restriction_classes=
-o smtpd_client_restrictions=
-o smtpd_helo_restrictions=
-o smtpd_sender_restrictions=
-o smtpd_recipient_restrictions=permit_mynetworks,reject
-o mynetworks=127.0.0.0/8
-o smtpd_authorized_xforward_hosts=127.0.0.0/8
-o strict_rfc821_envelopes=yes
-o smtpd_error_sleep_time=0
-o smtpd_soft_error_limit=1001
-o smtpd_hard_error_limit=1000
-o smtpd_milters=
-o receive_override_options=no_address_mappings''' % {"maxproc": configRegistry.get("mail/antivir/max_servers", "2")}
@!@
You have to recreate the master.cf by
univention-config-registry commit /etc/postfix/master.cf
I added a
service postfix reload
to make sure that the new configuration really is active.