/etc/postfix/sender_access:
domain1.com OK
domain2.com OK

Run: postmap /etc/postfix/sender_access

/etc/postfix/main.cf
smtpd_sender_restrictions = check_sender_access hash:/etc/postfix/sender_access, reject

/etc/init.d/postfix reload

https://wiki.centos.org/HowTos/postfix_restrictions