ESMTP service

[sisram2 () gmail com]

I'm looking for info on exploits and security of ESMTP when you telnet into
port 25. I understand how to telnet in and send email via the command line
but trying to understand the security implications of being able to do this.
I am currently looking at this on Exchange 5.5.

Does ESMTP from the command line need to be "accessible" for the apps to
work or enabled to troubleshoot?

Are their DDOS attacks or hacks against ESMTP?

Is there a best practice to secure ESMTP

I've been able find info about ESMTP (commands) but not much info on the
potential security risks.