Can send mail, but not receiving mail

I have a new hire who I configured a machine for. Earthlink handles our domain and e-mail. E-mail is working fine through them as he can check on the web. However, in outlook he can send mail but is not receiving incoming mail. All the settings are fine and in fact when I add his e-mail account to my outlook I can receive his mail. Does anyone have any idea why he isn't receiving mail? Does it have something to do that a previous employee was using that machine? I'm at a loss here as it seems as though it should be very simple and I've already wasted 8 hours trying to troubleshoot this.
Thanks.