A while ago, I wrote about MailTags. At that point it didn't work with IMAP accounts, so I couldn't use it. MailTags 2.0 is now in public beta, which adds IMAP support. It adds "X-MailTags" headers to the messages to keep the tag information.
I am hoping that I can use this to help keep track of the emails that I currently just "Mark As Flagged", for software that I need to upgrade, or other things that I need to be reminded of.
[via Hawk Wings]