/etc/postfix/main.cf
make sure you have included this:
hash:/etc/postfix/access,
in
smtpd_sender_restrictions = ................
Note you can also avoid receving to a specific domain if you add this also in reject_unauth_destination ruleset.
/etc/postfix/access
Have your domain listed like:
evildomain.tld REJECT outta.here REJECT
Then you need to generate the actual file that postfix will use = access.db like this:
# postmap hash:/etc/postfix/access
restart postfix and that’s it.