Apple Mail gets the job done, but there are a few crucial features missing. Rules can sort messages as they arrive, but Mail doesn’t offer much to help you organize messages after the fact. Indev Software’s Mail Act-On is a hugely useful Mail plug-in to do just that and much more.
In everything from Gmail to iTunes to the OS X Finder itself, folders are out—tagging and searching are in. It’s somewhat surprising then, that Apple Mail still hasn’t incorporated tags, even as OS X becomes increasingly adept at on-the-fly searching. Enter MailTags, a plug-in for Mail that allows you to assign tags to your email and thereby organize your messages.