Postfix uses the client to send out the game. Relay access denied appears and refuses to send the message

Solution:

Edit/etc/postfix/main.cn to find

smtpd_recipient_restrictions=permit_sasl_authenticated,
permit_mynetworks,
reject_unauth_destination,

Amend to

smtpd_recipient_restrictions=permit_sasl_authenticated,
permit_mynetworks,
reject_unauth_destination,
	reject_non_fqdn_sender,
reject_non_fqdn_recipient,
reject_unknown_recipient_domain