... chance that they’re spam.So howdoweuse this information to combat spam? postfix helps for the first three, butwe need other tools for the last.The rules for blocking unwanted messages are not included ... FQDN form.• reject_non_fqdn_sender:reject sender address that is not in FQDN form.Rejecting known spam domainsIf you have identified domains that you would rather not hear from again, use the formcheck_sender_access ... not available, theylook for an alternative system, and if none isavailable, theyretry delivery at a later date. Typically an MTAwill retry every 30minutes for fivedays before giving up.• Theyreceive...