This mailbundle allows for tagging emails and RSS messages on Mail3.0. It allows for keywords (tags) and notes. Funkydog can also search in these fields using OS X's metadata facility. Note, this does not add headers to IMAP mails - it only modifies the downloaded copy. Download the mailbundle(located in "Downloads") and copy the mailbundle to ~/Library/Mail/Bundles (create this directory if not already present)

Also remember to type (in Terminal)

defaults write com.apple.mail EnableBundles 1

defaults write com.apple.mail BundleCompatibilityVersion 3

Restart Mail.app.

If you would like to contribute code, feel free.

Incompatibilities

Incompatible with GPGMail (it conflicts with the GPG viewer on those emails which are signed or encrypted). It will still work but the tag view will compete with GPGMails encrypted/signed banner for those messages.

Incompatible with MailTags, since it uses the same kMDItem<> keywords for storing information. Apart from that I haven't tested it extensively with MailTags.

Features

You can sort on Tags, Notes and Steroids, the latter allows for any Metadata related query. All of these can be saved as Smart Folders.

Allows rules but unfortunately they can't be used part of the action. So you can test on Note,Tag (but not Steroids) and perform actions(the ones existing in Mail.app)

Issues

Yes, some outstanding issues(see "Issues") which I will try to fix.