what is the error message your getting from kmail/outlook?
time out or something esle?
have you sent a message from
you@example.com to
you@example.com or have you sent it from an alternative e-mail address? because if it's comming from the same e-mail address there could be a problem sending it, not reciveing it? Dovecot has got to be one of the simplest pop3 mail servers in the world to setup so i can't image that being the problem.