[Ubuntu Chicago] Best Email Client?

[Montel Edwards]

Good evening everyone,
 I've been looking for a good new email client for a while to use as
default, and I thought that there would be no better place than a
mailing list!

Here are a couple of things that i'm looking for:

1) Must NOT take up a lot of system resources ( I sold my Sun
Workstation, so all I have now is my netbook)
2) Must load quicky
3) Easy GPG Support
4) IMAP Support