Looking for a good IMAP email client

I've been using Netscape-communicator for email and generally like it,
except for accessing work email from home. I connect to work using "ssh
-X -C myhost". Netscape is _really_ slow through an ssh tunnel, even if
I've resized it to a tiny window.

Xcalc takes 3 or 4 seconds to show up; Netscape takes about a full
minute. Yuck. Any suggestions, especially ones that are easy, and can
be configured to do use an LDAP address book? I'm using Redhat 7.2 and
KDE if that's relevant. Oh yeah - having a spell-checker would also be
most handy :-)
TIA,

Steve