Hi:

I have a problem with sending emails to certain servers like hotmail, they get my emails as spam,
I've been looking around and I found that one reason maybe because my server is behind the firewall,
and the email messages are from a local IP rather that the public IP.
when using http://www.mxtoolbox.com I have got the following warning: "Reverse DNS does not match SMTP Banner"
I have configured the FQDN properly on my exchange 2003 server.

Thanks in advance

This is nothing to do with the firewall. Ask yourself:

Is your public IP static or dynamic?

What FQDN does the reverse DNS for this IP address resolve to? (Note: your rDNS record can only be setup by your broadband ISP.)

How does this compare to the FQDN configured in your Exchange server's Default SMTP Virtual Server?

Check out SPF to see if setting records can improve your emails credability. It just needs a little thought, and no cash