Is there an api that users can call to add / manage mail filters and autoresponders called by for example a PHP file?
Or do I need to edit files directly on the server?
For email filters I manage the procmail file I guess?
But where is the autoresponder file located? Or is that the same thing?
There isn’t currently an API that is user accessible. The administrator can use the Virtualmin API for some mail-related stuff, but not forwarders or autoresponders. Virtualmin does use procmail for most of the user-level mail processing tasks, and it is editable by the user, either on command line or in the Usermin GUI (if you grant them access to the procmail module; the default in Virtualmin is to provide access to the simple “Filter and Forward Mail” module, which probably handles what you need).
I’m about to start work on a Webmin CLI/web request API for the Webmin 2.0 branch…I’ll think on how we could implement something similar for Usermin (though the security implications are something we need to think more about when allowing a non-root user to use it).