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.