x400 email address – should I remove?

I have an exchange 2003 system and wish to set one of the users up slightly differently to the rest. We have a domain, let’s say ‘domain.com’ and this user has an email address within that.

All emails are directed to POP boxes by our ISP and the server collects these and distributes them accordingly. However, this particular user’s pop box is not accessed by the server, which then alows him to access his emails using the ISP’s webmail interface.

My question is this: How can I get the global address list in Exchange to send emails out to his external email address by default so that he receives internal as well as external email?

I notice an X400 type service in his exchange profile – should I remove this? If I do, will it then use the default email address for internal emails and therefore send the emails out to his external email address?