6. It must have a decent expiry system.
7. It must not be dog slow. I have big folders and I don't want to wait
5 minutes to load them.
Mutt suffers from 7, but it's not a big deal if you keep the number
of messages in a folder under control. For this I use archivemail, a nice
external program which can handle flagged and unread mail. I move read mail
to the archive after three days which keeps mutt under control.
Yeah, I've thought about using archivemail to take care of message
expiry. I don't care about archiving it--deleting it is fine--and I
assume archivemail can handle this.
I've resisted up to this point because I'm already using fetchmail,
postfix, spamassassin, procmail, courier-imap, offlineimap, mutt/gnus,
and emacs just to receive, read, and compose email. Yeah, UNIX
philosophy and all that, but you have to draw the line somewhere.