Show email by conversation through folders
I recently switched from Thunderbird to Evolution. There is an option in Thunderbird that you can select on any email and right click to view the conversation though all folders.
I use this a lot when a incoming email I need to see what I send them 3 emails back or where did I store the other emails of this subject.
Now I use a manual search on the subject in all folders, but this is not always accurate. Hope this is a feature that might get added.