Sending email via a LAN connection

Hi all.
Our office is running Windows Server 2003 and we are having problems sending email through the LAN. However, when the employees send through the same account at home, they don’t have any problem. I connected a laptop to the LAN but did not set it up as a user on the network and was able to send & receive mail,so the connection should be fine. What application permissions are related to email sending & what other things can I check?
Thank you,
Hilton
(I’m new to Server)