smtpd helo restrictions

From Initq

First, you will want to enforce the requirement for a helo to be sent for each message. Without a helo, you will not be able to perform any helo checks. You can do this by adding the following line to main.cf:

smtpd_helo_required = yes

smtpd_helo_restrictions =
        permit_mynetworks,
        check_helo_access hash:/etc/postfix/helo_access,
        check_helo_access hash:/etc/postfix/verify_helo,
        reject_unauth_pipelining,
        reject_non_fqdn_hostname,
        reject_unknown_hostname,
        reject_invalid_hostname,
        permit

Please read Restriction classes to understand the verify_helo.