Restrictions on recipient addresses
smtpd_recipient_restrictions
This parameter specifies restrictions on recipient addresses that SMTP clients
can send in RCPT TO commands.
    
        These destinations do not need to be listed in
        $relay_domains.
        
            The following restrictions are available (* is part of default setting):
            
                -  *permit_mynetworks: permit if the client address matches
                    $mynetworks.
                
-  reject_unknown_client: reject the request if the client hostname is unknown.
                
-  reject_maps_rbl: reject if the client is listed under
                    $maps_rbl_domains.
                
-  reject_invalid_hostname: reject HELO hostname with bad syntax.
                
-  reject_unknown_hostname: reject HELO hostname without DNS A or MX record.
                
-  reject_unknown_sender_domain: reject sender domain without A or MX record.
                
-  *check_relay_domains: permit only mail:
                    
                    Reject anything else.
                
-  permit_auth_destination: permit mail:
                    
                
-  reject_unauth_destination: reject mail unless it is sent
                    
                
-  reject_unauth_pipelining: reject mail from improperly pipelining spamware
                
-  permit_mx_backup: accept mail for sites that list me as MX host.
                
-  reject_unknown_recipient_domain: reject domains without A or MX record.
                
-  check_recipient_access maptype:mapname: look up recipient address, parent domain, or localpart@.
                    Reject if result is REJECT or "[45]xx text".
                    Permit otherwise.
                
-  check_client_access maptype:mapname: see
                    smtpd_client_restrictions.
                
-  check_helo_access maptype:mapname: see
                    smtpd_helo_restrictions.
                
-  check_sender_access maptype:mapname: see
                    smtpd_sender_restrictions.
                
-  reject_non_fqdn_hostname: reject HELO hostname that is not in FQDN form.
                
-  reject_non_fqdn_sender: reject sender address that is not in FQDN form.
                
-  reject_non_fqdn_recipient: reject recipient address that is not in FQDN form.
                
-  reject: reject the request. Place this at the end of a restriction.
                
-  permit: permit the request. Place this at the end of a restriction.
            
Restrictions are applied in the order as specified; the first
            restriction that matches wins.
                Specify a list of restrictions, separated by commas and/or whitespace.
                Continue long lines by starting the next line with whitespace.
                
                    NOTE: YOU MUST SPECIFY AT LEAST ONE OF THE FOLLOWING RESTRICTIONS
                    OTHERWISE POSTFIX REFUSES TO RECEIVE MAIL:
                    
                    reject, check_relay_domains, reject_unauth_destination