Here's my list of extensions for Thunderbird that you should take a look at. Note that I'm not the gatherer and hunter type when it comes to extensions. I usually prefer software that can do without extensions, plugins, skins, and all that other crap that will bog down your system and waste your time when all you want to do is work. The list is in no particular order.
- Buttons!
Buttons! will give you all those buttons that the Thunderbird developers forgot to add to the toolbar (and a couple more). The ones I like (and need!) the most are the previous and next buttons that will give you the next or previous email regardless whether it's been read or not.
- MR Tech's Toggle Preview Pane
Another indispensible button. Although I like to be able to do everything with the keyboard, I sometimes like to use the mouse (without finding my way through a menu first). This toolbar button will simply toggle the preview pane on and off. That's it. It's as simple as that. I have no idea why Thunderbird hasn't that one built in.
- Quick File
There. I told you I like to use the keyboard. Cleaning up my Inbox is something I don't do very often. When I actually do some sorting, I like to do it fast. With Quick File, it's just a key-down, short look at preview pane, and then a Alt-Q followed by some letters that are part of the name of the target folder for that piece of mail. The fastest way to archive messages to different folders.
- Minimize To Tray
Does what the name says. And you can even choose whether you can restore Thunderbird with a single click or with a double-click.
- Virtual Identity
Got a catch-all email account? And you use it to give different addresses to different people and organizations? Then you will sometimes find it hard to reply to emails because you haven't got a Thunderbird identity ready that uses the address it was sent to. Virtual Identity will take a look at the headers of emails you reply to and supply the correct From-address for you. And you can use it for new emails to quickly come up with a nice, new address.