Telnet and exchange

There doesn't appear to be a way to block telnet or any other sort of program from opening that port as long as it is open for use. I did a Google groups search and this subject has been beaten to death with the above conclusion.

Use the computer management pannel and look at the SMTP server, te properties of this node should contain a security options tab, using this you can limit the conections that can be made to a range of addresses (I.e your internal LAN) or a single machine (your mail server) you should block all other addersses from using this.

It sounds like your exchange server talks dirctly to the internet. This is a dangerous model. What you need to do is put exchange on an internal subnet. Next, put another mail server on your DMZ and configure it to relay for your mail domains. Be careful to set it up so that it only relays for your domains. This way, the outside world can only connect to your relay, and not your exchange server. Third party mail servers are rather cheap to purchase for relaying. Check out SLMailPro at www.seattlelab.com. It is rather inexpensive and feature rich. There are anti-spam and anti-virus features that you can add on also. This will also take a lot of load off of your exchange box.

Exchange can be configured to require smtp authentication. This would solve the issue