SMTPD Recipient Restrictions

These restrictions are useful for accepting, rejecting and even routing messages.

Reference: smtpd_recipient_restrictions in the postfix documentation

Example:

smtpd_sasl_auth_enable = yes
broken_sasl_auth_clients = yes
smtpd_sasl_security_options = noanonymous
smtpd_recipient_restrictions =
      permit_mynetworks
      permit_sasl_authenticated
      reject_unauth_destination
      reject_unlisted_recipient
      check_client_access pcre:/etc/postfix/dspam-filter.cf

NOTE: reject_unlisted_recipient is the best thing since sliced bread!
It will reject mail where the recipient domain is listed in Virtual_Mailbox_Domains but the recipient is not listed in Virtual_Mailbox_Maps. You would think this goes without saying, but this isn't the default behavior. When in doubt add this line!