Few notes about how to block a specific domain to send out emails

To help in cutting down the number of spam mails currently getting through a specific domain

# vi /etc/postfix/blacklisted_domains

# cat /etc/postfix/blacklisted_domains
mydomain.com	REJECT

# postmap /etc/postfix/blacklisted_domains
# postconf -e 'smtpd_recipient_restrictions = check_recipient_access hash:/etc/postfix/blacklisted_domains, permit'