how to stop using *telnet <domain> 25*

[Bill Campbell]

On Fri, Jan 23, 2004, Swapana Ghosh wrote:
...
> Someone is using one of our domain and sending mail from one valid user to
>another valid user under the same domain with the help of some of his own
>written script..
>
>Our server is not *open relay* but i want to stop to send mail by telneting
>with port 25. 

I don't think there's any way to do this as there's no way to tell the
difference between a telnet client connecting on port 25 and an MTA (Mail
Transport Agent) such as postfix or sendmail.

The SMTP protocol is pretty simple (after all it's Simple Mail Transport
Protocol :-).  It's trivial to enter any commands manually with a telnet
client, and a pretty common way to debug mail transport problems.  There
might be some way to detect mail allegedly coming from local users based on
the IP address of the connection, but (a) I don't know of a standard MTA
that would handle this, and (b) it would prevent your own roaming users
from sending mail from outside your network.

Bill
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