RE: SMTP Banner info

[Scott Klement <klemscot@xxxxxxxxxxxx>]

All telnet does is open up a TCP channel to a given port.  The only
difference between TELNET and SMTP in that respect is that TELNET
prints everything it receives on the screen, and sends back whatever you
type, where SMTP is normally automaticallly handled by a program.

For _ANY_ TCP service, you can telnet to the port number of that service,
and carry out the protocol manually if you like.

If you block it with a firewall, you block everything from being able to
connect to it -- including legitimate mail clients.

Even if you could just block telnet clients (which you can't) it wouldn't
help, because someone could just write their own special e-mail client
that does nothing but retrieve that string.   Either way, it's visible to
the outside world -- if that's not a security risk you're willing to take,
you need to turn it off in the server itself.


On Fri, 19 Apr 2002, Mark A. Manske wrote:
>
> Just to be a pain, why can someone telnet to your mail service?
> You should not allow that at the firewall.
> Just speaking from a security viewpoint.
>