Help needed on block SMTP

[shyam hirurkar <shyamph@gmail.com>]

Hi All,

I have a mail server running on Qmail and a gateway running on
IPtables on kernel 2.4.26.

Now my question is:
I want to block SMTP port on the firewall. Also allow only SMTP
connection to my mail server.

Thanks in advance.
Shyam