This is very useful example howto reject an external email address from sending mail to our users.

su – zimbra

[zimbra@mail ~]$ vim /opt/zimbra/conf/zmconfigd/smtpd_sender_restrictions.cf

add on the first line

hash:/opt/zimbra/postfix/conf/reject

create the reject file

[zimbra@mail ~]$ vim /opt/zimbra/postfix/conf/reject
[email protected] REJECT
spamdomain.com REJECT


[zimbra@mail ~]$ postmap /opt/zimbra/postfix/conf/reject

[zimbra@mail ~]$ zmmtactl stop && zmmtactl start
/postfix-script: stopping the Postfix mail system
Stopping saslauthd...done.
Rewriting configuration files...done.
Starting saslauthd...done.
/postfix-script: starting the Postfix mail system


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