How to access webmail to the mail offline server?

Hi experts,
I have setup a mail offline server (MDeamon). My small network is connected to internet via ISA server with ADSL line. I have created an account on Dyndns but I failed to register a mail.abcd.com pointing to my computer. it seems that the tcp address has been filtered by the ISA. Can anyone help me solve this problem?
Any solution for this matter is highly appreciated. my email is datquan362@yahoo.com.
Quan