coplaniuk wrote:1) It has to support IMAP.
2) It has to be cross-platform -- I run both Windows and Linux on this machine, and don't really want two clients if I don't need it.
Thunderbird/seamonkey, (al)pine, or mulberry if IMAP, cross-platform, and stability are priorities. Mulberry is proprietary but gratis. alpine is the classic pine under the Apache license. Since I prefer F/OSS, I use alpine + thunderbird. I've use seamonkey off-and-on. I prefer their community over TB's corporate development. However, TB's new features often draw me away. I used to use mulberry. If you are O.K. with proprietary software, it is a great IMAP client.
Thunderbird would be the obvious choice, but I'm growing tired of its quirkiness. There are tiny little annoyances that I have grown to dislike.
What would those be?