Unable to access POP3/IMAP via SSLVPN

Hi all,
Email clients------SSLVPN Gateway--------Email Server

I have some Email clients present on the back of the SSLVPN Gatway. I
use IE to login to the SSLVPN Gateway and proceed with the application
access. The SSLVPN Gateway just proxies the requests towards the Email
server port no 110(POP3). My Email clients does not give error when
they send and receive any mail. But whatever I send its not received
on the
Email server. Its going to a Black Hole. Without sslvpn its working
Fine.When I manually telnet to the Email server via 25 port no. its
saying "unable to relay to the destination mail address".Please let me
know what might be the reason for this failure.I see the same behaviour
with IMAP also.Please provide me some links for my Linux configuration.
Thanks
sasi