Longtime Gems readers know I'm a big fan of , and the latest such plug-in I've found, , provides exactly that feature.

Once you install MailTabs, any Mail action that would normally result in a new window--composing a new message, replying to a message, opening a message in its own window, opening a new main Mail window, and so on--instead opens that window in a that appears in a new tab bar just below Mail's toolbar. As with your Web browser, you can drag tabs to the left or right to reorder them, although you can't drag a tab off the tab bar to open it in a separate window. (In fact, with the current beta version of MailTabs installed, I couldn't find any way to open a second window--everything opens as a tab. Hopefully this capability will be added as MailTabs gets closer to an official release.) To close a tab, you just click its close (X) button.

Because even a new main Mail window appears as another tab, you can use MailTabs to keep multiple mailboxes open within the same window, switching between them as needed. And, of course, you never have to deal with the hassle of finding a particular message window hidden behind other windows--they're all listed neatly on the tab bar.

MailTabs is currently in the beta stage, so it's far from being complete. For example, in addition to the issue mentioned above, there are no keyboard shortcuts for navigating between tabs, and you'll see some visual oddities such as the Mail window disappearing for a half-second whenever you send a message. I'd also like to be able to choose the width of tabs, so more of each message's title appears in its tab; to choose on which side of the current tab new tabs open; and an option to keep Mail's mailbox sidebar visible at all times (it's currently visible only in tabs hosting a mailbox view).

I'm looking forward to the official release of MailTabs. It won't be for everyone, but it's a Promising Prospect that brings a much-requested feature to Mail.