Signature blocking telnet to SMTP server

[admin_2]

Is it possible to block telnet to SMTP server from port 25 with IDS. I want to create a custom signature for this but I don't know how. If I write as hello it will block all.

[#2]

You mean you want to prevent people from interactively telnetting to port 25, but still allow regular SMTP mail through?

Sorry, that's impossible. There is _NO_ difference on the wire between those two operations, so there's nothing you can select on to permit or deny.