This is a nice little MUA for Unix/X11 based on the GTK+? (1.x series) widget set. It's simple, fairly quick, and Just Works (in particular it doesn't need, but can use, an external MTA).
Another major advantage (from my AntiBloat perspective) is that it doesn't depend on the assorted GNOME libraries, a GTK+? installation is all that is required.
does it do imap? -- 
PerryLorier
Yes, Sylpheed does support IMAP. It's not exactly brilliant in the main release (no filtering, things like folder existence can get out of sync), but in sylpheed-claws, (sort of the development branch) it seems better - at least filters work on IMAP.
2 pages link to Sylpheed:
http://sylpheed.good-day.net/