Developer reply by Ryan Lee
Rated 3 out of 5 stars
I initially thought Spamness wasn't working because it wouldn't sort an existing folder but it does a good job of sorting newly received mail.
This review is for a previous version of the add-on (0.1).As noted in the extension description, Spamness can only work on folders that existed before its installation when you re-index them. There should be a better way to indicate that after installation, though, so I'll be looking into how to make that more clear.
To create your own collections, you must have a Mozilla Add-ons account.