This is really needed, there is/was a plugin that did this but it was really buggy, needs to be able to set auto-archive using similar settings as retention / compacting. Some folders I am happy to compact and delete old email, others I want to keep ...
This is really needed, especially in the favourites pane. I used to be possible with a plugin but this is now not compatible. Maybe they will update the plugin but better if it was part of the core.
