[expert] X Mail Client

[Expert User]

I need a fast and robust mail client which can handle multiple IMAP/POP 
email accounts with large number of folders and big volume of mail.

Mozilla mail is almost there, but Mozilla takes too much memory, crashes 
sometimes and on my Celeron 433 system, it is rather sluggish.

KMail is better in speed and memory foot print but doesn't have IMAP 
capability.

Do you have any other suggestions?