How would it be possible to make a global sieve filter rule on ISPConfig 3.1? I would like a rule to automatic put SPAM-tagged emails into the Junk folder on each mailbox existing on the server.
Edit the global ispconfig sieve template file and store your custom copy in the conf-custom sub folder.
copy /usr/local/ispconfig/server/conf/sieve_filter_1.2.master to /usr/local/ispconfig/server/conf-custom/sieve_filter_1.2.master and edit it there. The file affects all new and updates mailboxes.
This template is used to create all filter files. To apply it to all existing mailboxes, use Tools > resync in ISPConfig.
As @till says, that is the template for all user's sieve scripts; a different solution is a true global sieve script, which you could configure with custom dovecot config. There's an example in https://wiki2.dovecot.org/Pigeonhole/Sieve/Configuration or similar comments in /etc/dovecot/conf.d/90-sieve.conf -- you will need to change /etc/dovecot/dovecot.conf though, as ispconfig doesn't use the conf.d files, so to make your changes permanent you need to put them in a conf-custom template (ie. /usr/local/ispconfig/server/conf-custom/install/debian6_dovecot2.conf.master) similar to what's described above (get the original debian6_dovecot2.conf.master from the install tarball or git).
Thank you @Jesse Norell . This is more like the solution i was looking for, though Till's answer did help me alot.
Yes, whenever they are generated. You can go to Tools > Resync to force that to happen for all accounts.