how to protect telnet access to smtp port 25?

Posted by Michael Mao on Server Fault See other posts from Server Fault or by Michael Mao
Published on 2010-12-25T01:29:02Z Indexed on 2010/12/25 1:55 UTC
Read the original article Hit count: 544

Filed under:

security

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firewall

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smtp

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telnet

Hi all:

Please consider the following:

192-168-1-106:~ michael$ telnet <remote_server_ip> 25
Trying <remote_server_ip>...
Connected to li*****.linode.com.
Escape character is '^]'.
220 mindinscription.net ESMTP Postfix (Ubuntu)
quit
221 2.0.0 Bye
Connection closed by foreign host.

Is this very bad? how to protect port 25 from malicious attackers? I've already set up a firewall, but not very sure what to do in this case.

Basically I'd like to use this server to only send emails as alert messages, not receiving any external emails.

Many thanks to the help in advance.

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