Review for Copy Folder by SireBelch
Rated 1 out of 5 stars
NOTE: THIS HAS BEEN UPDATED IN A NEW PLUGIN!
I can confirm from a post elsewhere in this thread that someone else has updated the plugin and it works great with new versions of Thunderbird!
https://addons.thunderbird.net/en-us/thunderbird/addon/copy-folder-mod/
To create your own collections, you must have a Mozilla Add-ons account.