MailTags Now it adds all this stuff:

[new] Added MailTags icon column to list view (Ctrl-mouse click column headers to add column) All messages with tags will show with a tag icon in this column. [new] Added “Show Note As Subject” option to messages tag panel. Notes will show as italicized subjects. [new] Added Toolbar item for toggling tag panel (Customize toolbar to add button) [new] Added preference option to show or hide the message area’s MailTag icon. [new] Added new menu item “Tag this message” (cmd-ctrl-t) that will take focus to tag panel (opening panel if necessary) [new] Can now tab through tag panel and use arrow keys for menu selection.

For all your mail-tagging metadata needs.

status: published
lastmod: '2006-11-07T01:33:54.000Z'
author: John Stansbury
cms: wordpress
custom:
  podPressPostSpecific: 'a:6:{s:15:"itunes:subtitle";s:15:"##PostExcerpt##";s:14:"itunes:summary";s:15:"##PostExcerpt##";s:15:"itunes:keywords";s:17:"##WordPressCats##";s:13:"itunes:author";s:10:"##Global##";s:15:"itunes:explicit";s:7:"Default";s:12:"itunes:block";s:7:"Default";}'
  _utw_tags_0: 'a:2:{i:0;O:8:"stdClass":1:{s:3:"tag";s:3:"gtd";}i:1;O:8:"stdClass":1:{s:3:"tag";s:15:"software-update";}}'
  similarterms: panel added column show icon mailtags messages menu toolbar item message option preference hide area cmd-ctrl-t selection mail-tagging metadata keys