Unable to recieve e-mails anymore

The nameserver information for our domain (mcaulifferegional.org) was recently updated at our registrar and shortly after we are unable to recieve external e-mails anymore. We can send and recieve e-mails internal fine, as well as sending e-mails out.

Access to OWA also stopped working as well at the same time (mail.mcaulifferegional.org/exchange) and tsweb.

Does anyone have any thoughts on what needs to be updated for the server-side configuration?

We’re running Server 2003 SP1 and Exchange Server 2003 SP1.

I would appreciate any help. Thanks.