For Mail power users, Act-On is a must-have. Go. Download. Now.

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. Using rules and user-configurable keystrokes, Mail Act-On can easily tame even the most unruly inbox. And compatibility with Indev’s MailTags (4 Stars, Sept/08) turns Mail Act-On into an organizational powerhouse.

At its core, Mail Act-On is a keyboard-based front end for Mail rules. Act-On will allow you to invoke rules on the fly via a pop-up menu or with a custom keystroke. After installing the plug-in, your Rules pane in Mail Preferences will sport three tabs. Inbox Rules will show all your standard Mail rules. Outbox Rules will show rules for sent messages—handy for separating your outgoing personal messages from work-related ones or keeping related messages together. Keystroke Rules (our favorite feature) are rules that you have designated to run when you use a custom keystroke. We found them most useful as a method for quickly filing messages into the appropriate mailbox.

Even with our relatively flat structure of only a few mailboxes, being able to easily separate out the actionable emails from the press releases and interoffice messages without leaving the keyboard allows us to whizz through our overstuffed inbox. Act-On makes it easy to navigate mail. Hitting F1 activates the plug-in’s floating window, where you can apply rules, move or copy messages, or navigate to specific mailboxes. The window also searches as you type, making navigating complicated mailbox structures or lengthy rule lists incredibly easy.