Outlook can only receive mail from ports you set up on your server for that purpose.
Are you running your own DA server? If so you should be using the Authenticated Email Submission port to send email.
You can change your system configuration so POP and IMAP would listen on different ports, but then you'd have to notify everyone, as the standard ports wouldn't work. I'm not sure how to do it.
Or of course you can read your email through one of the webmail clients.
Jeff