Ability to duplicate a mail filtering rule to create a new one
Sometimes I create fairly complex filtering rules in Evolution's "Edit > Message Filters", and there are cases where they need to be separate filters to account for some special variant of a combination of rules… however it is painful to create multiple such filters right now, because the filter editing dialog is modal (you can't open multiple ones) and you have to remember and manually transcribe/configure everything everytime.
It would be much easier if there was a "Duplicate…" or "Inherit…" button that acts like a hybrid of the Add and Edit buttons: clicking it would open a new filter Add dialog, but with its properties already pre-filled to match the previously selected filter; the user would have to enter a new name and change some properties (in conditions or actions) before the "OK" button would become sensitive (on that note, the "OK" button should also be insensitive in the "Add" dialog when the user has not specified any valid conditions and actions).