I use a kind of roundabout way to move my Outlook clients to Evolution.

Outlook has probably snarfed all messages using pop3.  I configure the mail
server to use imap, and reconfigure their client to use imap instead of
pop3.  I then have them move all their messages back to the server using
imap folders.  Once that is done, they can then donwload the messages again
using pop3.  Or just keep using imap - that's what we do here and it ensures
that SquirrellMail works correctly.
--
Thomas Cameron, RHCE, CNE, MCSE, MCT
Cameron Technical Services, Inc.
http://www.camerontech.com/
(512) 454-3200