Sometimes, you find an application that “just works” for you, and that’s it — no further exploration required. For instance, after I got Vim figured out years ago, I’ve had very little need or motivation to really examine other text editors. (Excepting writing articles comparing text editors…) I’ve also been really happy with Amarok, WordPress, Pidgin, and a handful of other apps that I use frequently that I’ve just had no reason to want to switch to another application.
And then there are email clients. 
I’ve tried ‘em all… from Pine to Thunderbird, Mutt to Gmail, I’ve just never found a single email client that I’m 100% happy with. Perhaps that’s because I spend SO MUCH time in email, I have many occasions to think “wow, this feature is really cool, but I wish I could do XYZ more effectively.”
For instance. I’ve set up Google Apps for my Zonker.net domain, which I use for almost all of my correspondence. In a pinch, I think Gmail is great. I can even get by with it for a long stretch, but it’s really not optimized for my type of work — where I might want to eyeball three or four messages simultaneously — so I don’t like working in the Web-based email client all of the time.
After an extended stretch of using Gmail, I’ve decided to give KMail another shot. I’m using in on openSUSE 10.3, we’ll see how that works out.
I’m curious about what other folks do that works for them. Your mail clients, tell me about them!
I use claws-mail here… it’s fast, it lets me do everything from the keyboard and it looks pretty nice too.
Let us know how it goes with KMail. I recently moved from Thunderbird to Evolution and am enjoying the integration with Spamassassin.
Mail clients are the bane of my existence. I get hundreds of emails per week, have tried a zillion clients, and well, they all suck in their own way. The cool feature in client A isn’t in client B but it has something else cool instead, etc. And Gmail? Ugh. Though I use it as my primary address, reading it on the Web (vs. POP-ing it to a client) is terrible. The worst thing is not having access to any other emails if you’re composing one — unless you’re willing to save to draft, click over to the inbox, click back to drafts, etc. Boo…hiss…
So. Right now I’m using Mail.app and tolerating it. I’ve tried Mailplane (the Gmail overlay), Mailtags, smart mailboxes, etc. but pretty much all I have going on right now is a million folders and two million Rules. Of course, this doesn’t help when I’m working on the laptop though. If dotMac ever started letting users sync Mail.app across computers, I might collapse from the bliss. Until then, I struggle.
I’ve just migrated from Evolution to Thunderbird. I am using Gmail via IMAP. The GMail’s spam filtering function free me from considering the spamassassin. I rarely use Calendar, Notes, etc. What I want is exactly a popular email client, that is Thunderbird.