dial-up + VPN cannot contact the Exchange 2003 server

[lambent]

I'm using Outlook 2003 and I have 2 ways to connect to my office:

A) Broadband + VPN
B) Dial-up + VPN

Both (A) and (B) can ping the Exchange 2003 server IP address. However only (A) can send/receive emails. (B) can't contact the server and so cant send/receive emails.

Anything necessary configuration required on the Outlook 2003 to do the job?

Thanks