How to restrict incoming mail in Postfix.

Scenario: We have some discussion groups (alias) and we want only a few internal people in the field to have access to them and the rest of the internet and internally are not allowed.

We are supposed to have:

postfix on linux ( centos or debian )
minimal knowledge of linux
I know how to use a cli editor like vim or nano

Our domain: covaci.tk
alias: [email protected] and [email protected]

1. First Step Setup list to restrict.
vim /etc/postfix/main.cf
smtpd_recipient_restrictions = check_recipient_access hash:/etc/postfix/protected_destinations .................... .................. ...the usual stuff...

Here we have defined a class for each alias.

And in these files who has the right
to send mail and the rest rejected (in /etc/postfix/main.cf ).
smtpd_restriction_classes = local_only smtpd_restriction_classes = local_only2 local_only = check_sender_access pcre:/etc/postfix/restrict_intern local_only2 = check_sender_access pcre:/etc/postfix/restrict_intern2

2. Second Step create files
vim /etc/postfix/protected_destinations
[email protected] local_only [email protected] local_only2
After you exit the file you're running postmap /etc/postfix/protected_destinations

vim /etc/postfix/restrict_intern
/[email protected]$/ OK /[email protected]$/ OK /.+/ REJECT

If you want a custom error message:
/.+/ REJECT "This is a custom error messages created by Admin Team at Boss request!"

The rule in this file says that only user [email protected] and [email protected] have the right to send the rest of the mail are rejected.
vim /etc/postfix/restrict_intern2
/[email protected]$/ OK /.+/ REJECT

And finally get restart services
/etc/init.d/postfix restart ( sysV systems like Centos 6) or systemctl restart postfix ( systemd system like Centos 7)

If you get some errors look at /var/log/maillog and test if works!
Source: http://www.postfix.net/RESTRICTION_CLASS_README.html

@luciancovaci
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Created on 20170908 at 17:41 EET