Something

root@ashley:~# postconf | grep restrictions
smtpd_client_restrictions = 
smtpd_data_restrictions = reject_unauth_pipelining, permit
smtpd_end_of_data_restrictions = 
smtpd_etrn_restrictions = 
smtpd_helo_restrictions = 
smtpd_recipient_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_invalid_hostname, reject_non_fqdn_hostname, reject_non_fqdn_sender, reject_non_fqdn_recipient, reject_unknown_sender_domain, reject_unknown_recipient_domain, reject_unauth_destination, permit
smtpd_sender_restrictions = reject_unknown_sender_domain