[Exim] Exim, can send mail but not receive

Just installed Exim 3.35, I can send mail from the server and from a machine
on the LAN. The machine has the domain MX record pointing to it. The
/var/mail/$user user files receive the mail but clients seem incapable of
collecting this mail. Using outlook express, get the following

Your server has unexpectedly terminated the connection. Possible causes for
this include server problems, network problems, or a long period of
inactivity. Account: 'LANMAIL', Server: 'mailserver_name', Protocol: POP3,
Port: 110, Secure(SSL): No, Error Number: 0x800CCC0F

What do I need to do to allow mail to be collected

Many Thanks

Gordon Chapman