[Exim] error message

I've got exim set up and running great on my home network, but a friend of mine wants a email address that he can use over his dI have configured wrong. he gets the following error message when he tries to send out of my smtp.

The connection to the server has failed. Account: 'cro.wox.org', Server: 'cro.wox.org', Protocol: SMTP, Port: 25, Secure(SSL): No, Socket Error: 10051, Error Number: 0x800CCC0E

any suggestions would be appreciated