Currently we can assign per folder processing that is executed at startup, display and on request. However it would be very useful to permit additional processing triggers, e.g. insert into folder. Adding additional trigger would require probably small revamp of processing setup. Currently processing triggers are specified globally for all folder actions in folder Properties dialog. Triggers should be processing entry specific, similarly as filters are assigned to account. User could select if specific entry should be executed on specific trigger or some predefined set of triggers, e.g. ALL, Startup, Entry, Insert. Use case, per folder notifications on receiving mail (i.e. messages of specific person, failure notifications).
When you let insertion into a folder trigger processing rules, you have to do some kind of loop-detection.
Can you be more specific what you mean by loop-detection? Do you just mean here something like moving message between two folders?
Yeah, bouncing messages. Folder A sends the message to Folder B, which sends it back to A, which sends it back to B, until eternity. When those chains get more complicated, it's not entirely trivial to detect such loops.
Solution may be as simple as defining trigger as "Filter Insert/Move".