Use MailTags convenient side panel to add tags keywords, project, priority, notes to your messages. Use contextual menus to tag several messages at the same time. All of MailTags interfaces feel built in, not added on.
Limitations: 21-day trial.
Requirements:
OS X 10.5 or later
Version for 10.4.7 or later is available
here.
Spotlight must be enabled
Author's Site
MajorGeeks TX
Internode
Screenshot
