Never had a problem with incoming setup on Mail.app
INCOMING ACCOuNT INFORMATION
POP3 server
Incoming server mail.yourdomain.com
username
you@domain.compassword whatever
->ADVANCED TAB
Port 110
USE SSL unchecked
Authentication password
OUTGOING I usually use my ISPs mail server, but I've also used LPs
This is my home 10.6 settings, if I remember correctly my 10.4 work setup is worded a little differently . . .
server name mail.yourdomain.com
->ADVANCED TAB
USE default ports
Use SSL checked
Authentication password
username your account username
password your account password
hth