external vs internal port lacking documentation

[Lecaf_]

aaaarg spent an hour on this

port 25 refuses to relay from RFC1918 addresses without any meaningful error
what you get is :
Jan 07 15:23:38 pmg postfix/postscreen[752]: NOQUEUE: reject: RCPT from [192.168.1.126]:64446: 550 5.5.1 Protocol error; from=<me@gmail.com>, to=<me2@gmail.com>, proto=SMTP, helo=<u>

port 26 happily does relay from RFC1918 addresses
Jan 07 15:24:29 pmg postfix/smtpd[1088]: NOQUEUE: reject: RCPT from Psyche.localdomain[192.168.1.126]: 554 5.7.1 <me@gmail.com>: Relay access denied; from=<me@gemail.com> to=<me@gmail.com> proto=SMTP helo=<u>
(here it was rejected of course because of course I'm not google)

to test with telnet you need to come from outside like a free web based telnet client (disable greylisting btw)
Jan 07 15:37:04 pmg postfix/smtpd[1693]: NOQUEUE: reject: RCPT from unknown[149.28.194.172]: 554 5.7.1 <me@gmail.com>: Relay access denied; from=<mc@lalala.com> to=<me@gmail.com> proto=SMTP helo=<u>
(again I'm not the google postmaster denied relay is ok)

could have that in the documentation would have spared me my time.

 

[Stoiko Ivanov]

port 25 refuses to relay from RFC1918 addresses without any meaningful error

it does not refuse relaying from RFC 1918 - the issue is that postscreen:
https://www.postfix.org/POSTSCREEN_README.html
detects the tests as breaking the protocol

port 26 happily does relay from RFC1918 addresses

postscreen does not operate on the internal port - which is why the tests pass there