Telnet and Exchange

sending to your internal people? Yea, I'd install some spam filtering software. you cannot stop access to port 25 since that's how email works. Hope this helps.
Pete

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.

Telnet is a Text based terminal program, and it lets you specify what port to connect to. If you run an Email Sever than someone will be able to use Telnet as the sending host by connecting to port 25. Since SMTP runs on port 25, and SMTP is a text based protocol, therefore Telnet to port 25 will allow one to send email to the SMTP host.
How do you know s/he is using Telnet? they could design a SMTP host to do it, why would they use telnet?
Unless you know who it is, what about blocking his IP address?
If it is spam just use a spam filter.
If s/he is doing anything illeagel (id theft, etc.) then contact your local Law Enforcement.
Try to report then to their ISP (upstream provider for ISPs).

The only way that I have successfully done this is with a PIX515 Firewall ver.6.1 using the mailguard feature. It reduced the SMTP commands to a bear minimum. When telnetting to port 25 on the outside (translating through the PIX) you get gibberish. I have not been able to successfully send data to another user on my mail server. So far it seems to do the job.
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_data_sheet09186a0080091b15.html

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