Outlook 2003, can't receive hotmail messages... (Not pop hotmail just any message sent by anyone from '@hotmail.com'

Okay...

Here's a weird one.

User, can't receive messages from @hotmail.com email addresses. User is not a hotmail user, and I've gone through the entire email gauntlet from source to firewalls,  to spam filter, to exchange servers and back again. The spam filter MX logic confirms all of my hotmail test have been delivered to the system in question.

At no point have any bounce back messages been received.The initiating users in hotmail, never receive anything... To them it looks as though the messages have been delivered without error.

MS Office is on its most recent service pack, and windows is at service pack 3.

Client uses pop mail account set up within outlook 2003.
There are currently no add-ins enabled in outlook2003, the local AV has been disabled (thought maybe the AV was interfering with mail reception)

Client can receive mail from any other source, except hotmail.