[rhn-users] Blocking SMTP from telnet

[cbeerse at lycos.nl]

jijo john wrote:

>  
> Hai
> I have a mailserver(sendmail) i want to block telneting to my smtp server
>
> #telnet myip 25
>

It is easy to block telnet to the server, that's just blocking (or 
better, not answering) the port.

It is verry hard to see for a port to see what app is calling. It is 
more or less in the response.
With verry old sendmail implementations, it is relatively easy to just 
send a message with telnet, the sendmail just swallowed about everyting

Current  sendmail implementations have some handshakes to see if it is a 
reasonable mail-client out there but then, that is also verry eays to 
implement since it is a public-known and well documented protocol. Even 
Micro$oft managed to implement it good enough in outlook and outlook 
express.

Hence, you better do as most isp-s: use accounting and only accept from 
known IP-addresses.

>
> I want to block or only secure user can access this
> how can i do this ?
> thanks in advance
> jijos
>
> jijo's
>
>
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