I'm altering the file main.cf to define the correct set of rules in order to block telnet on port 25 or at least require authentication when someone uses that command.
I've googled for a while and after reading some guides I've understood that there are 3 kind of postfix restriction classes.
If I try to do a telnet on port 465 or 587 it directly cuts my connection when i digit the HELO command. I'm trying to replicate the same behaviour when I use telnet on port 25. If I close port 25 I don't receive emails anymore.
In our infrastructure is not possible configure a external smtp relay.
The server now works perfectly on sending/receiving mails.
Thanks in advance,