I am trying to deny access to anyone using telnet to my SMTP server.

So far I've shut down xinetd, but the connection still comes up as if I did nothing.

Any suggestions would be greatly appreciated!

xinetd has nothign to do with smtp, why did you think it did?

you can't (easily) block access from a telnet client to any tcp port, i guess you're not really clear on what the use of telnet in that situation is. telnet in itself is an extremely simple client, which does virtually nothing. the only slightly "clever" bit is the server which spawns a login shell on the telnet port when connected to it. as the client is so simple, it can be used in many different ways to troubleshoot servers and netwrok connectivity. it basically just allows a human user to interact with whatever serivce is connected to a tcp port. when used in this way, it's really *not* telnet at all, just a pipe to a tcp port.

as you're hopefully aware telnet is regarded as a huge security risk, and i'd assume that's why you wish to stop it here, but the risk is actually the use of the client and the sever and the way a login esssion works across the two, not the client itself at all.

basically don't try to block it, there's no point and i'm not really even sure it's possible as telnet clients don't really identify themselves in any way at all on connection, they just send whatever keypresses you make and show you what the server replies with, hence it's many many uses debugging smtp, http, etc...

You can't stop it as far as I know, and there is nothing unsafe about people using a telnet client to access your mail server. It's the telnet server which is unsafe and you are shutting that down with xinetd.

Chris,

I am quite aware that xinetd has nothing to do with SMTP. But, using Telnet you can access the SMTP server. Go here for an example -- http://www.pantz.org/email/misc/smtptelnet.shtml.

What I am trying to do is restrict access to that. In other words, I do not want anyone using telnet to connect to the SMTP server. So my questions remains, how do I do this? Setting in qmail-smtp? Firewall settings? Shutting down xinetd?

Thank you in advance for your help.

You can't stop it

did you not read what i wrote?? I'm a network architect, i spend all day working with ethernet and tcp/ip. i know what the issues are here, and going by your reply you really don't understand your own question. maybe if you wish to keep persuing this, actaully give a reason as to why you think this is a bad thign to do.

use iptables to block it... or tcp wrapper...

no, you didn't read the question correctly. what he wants is not possible. unless you wish to provie otherwise with an example that is...

In SMTP, there is two type of relay.

If your SMTP service is in open relay, any one can use your SMTP server to send mails. To resolve this we need to change the relay to closed relay. If you did like this you can safe guard your SMTP server and all of them can get response from port 25 but they can't use your service to send mails without authorization.


Regards,
JP