Thanks Raz for the suggestion with regards to the below mentioned problem, but my ISP MX records are already pointing to my server IP address. This works without a firewall. But after implementing the firewall it stops receiving mail. I believe I have to allow ESMTP or SMTP on a port. This firewall is windows2000 based.
Can you guys help.... I have no time...

(....I am implementing an Internet Security and Acceleration (ISA) firewall on my network. I want to know the protocol (ESMTP or SMTP) port to open to allow my ISP Linux server to relay mail to my Linux server across the firewall.
If anyone may help.....!!!!...)

As I said in my last 2 replies it's port 25.

Allow incoming connections from anywhere to destination port 25 on the firewall.

ESMTP is just the enhanced version of SMTP and also uses the same port. "your client will first try ESMTP then if EHLO doesn't respond it will use SMTP"

/Raz

Thanks Raz. it has worked.