After setting up Mozilla Thunderbird 3 on my netbook, one of my favourite e-mail clients (alongside KDE's good old KMail), and finally managing to get it to behave, I thought I'd share some tips. I'm using Thunderbird 3.1.10 as shipped by Ubuntu.
Let my server do the spam filtering, okay?
I have a well-trained spamassassin set-up running on my own IMAP server, which takes care of filtering spam out of my inbox, and learns from a "spam" folder I populate by hand (and with a honeypot). Now Thunderbird has its own junk mail controls, and it is actually possible to teach these to play along.
First of all, I want Thunderbird's prominent "junk" button to train good old spamassassin, not just its own filter, by moving messages to the designated spam folder: in Preferences → Security → Junk, select When I mark […] Move them to the account's "Junk" folder.
The next problem is telling Thunderbird that the "Junk" folder is not actually called "Junk". This is done in the account's settings, on the Junk Settings page. Here, you can not only select the folder junk goes into, but also turn Thunderbird's own filter off, in case you're like me and think that one spam filter should bloody well be enough.
When I say delete…
By default, when you delete a message in Thunderbird, it isn't "expunged" until you close the program. This has the unfortunate effect that, when you (re)move messages on one computer, leave it on, and check your inbox on another computer, or your phone, those messages will still be there. This can be extremely confusing, or, at the very least, somewhat annoying. There is a (well-hidden) solution, though (thanks, Ryan): set mail.imap.expunge_after_delete to true in the config editor (Preferences → Advanced → Config Editor).
My archive is my castle
Changing which folder to use as an archive folder is fairly straightforward: it is set on the same configuration page as the "Sent" folder, in case you need to change that: Copies & Folders in the account's settings.
Thunderbird, by default, splits the archive up by year. I'm fine with this setting myself, but I've done some digging and it appears that there are some hidden configuration options to change this. A few weeks ago, Jim Porter added a graphical configuration screen to the upstream Mozilla source code which I expect to see in a release soon. (bug/commit)
Woah, you want to index everything?!
Thunderbird's global search is, in principle, a great feature, but there are some things I just don't want to see when I search for specific messages. This is, especially, spam, and I also like to keep my mailing list archives separate from the body of mail I may want to search. Luckily, Thunderbird lets you exclude specific folders from the global search in the individual folder's properties.
E-Mail is an inherently insecure medium, even if you don't use Yahoo! mail. The situation, however, can be vastly improved by using the (comparatively) popular GnuPG software. For Thunderbird, you'll want the Enigmail extension. I won't waste any more words on it here as it has an excellent configuration wizard and I'm sure you can find more information without me if you want or need it.
Consider the android
Since I got an Android phone, my contacts have lived in Google's ominous data banks. My phone can synchronise with Google, and, as it turns out, so can Thunderbird! The extension I'm using is called Google Contacts (unimaginative but obvious), and it works like a charm. It creates a new address book and takes care that it stays synchronised with Google, both ways. It even supports multiple Google accounts, for the double-faced among us.
That's it for today. Feel free to leave feedback and suggestions in the comments.