Postfix: How to secure port 25? [duplicate]

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How can I secure port 25 in postfix/dovecot? Right now, I can send internal email through telnet without login. For example:

telnet mydomain.com 25
MAIL FROM:<me@mydomain.com>
250 2.1.0 Ok
RCPT TO:<you@mydomain.com>
250 2.1.5 Ok

Right now, everyone can send emails without login.
All I want is that, emails can only be sent when user logged in.

How can I make it something like “Relay access denied” if I am not logged in.

Answer

This is the postfix mynetworks option. You probably want to set it to 127.0.0.1/32, that way only programs running on your server can send mail without logging in first.

Attribution
Source : Link , Question Author : Maximilian , Answer Author : Law29

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