Unverifiable return paths
Mailtraq performs this check to see whether it is technically possible to reply to the inbound message. If the message claims to be from an address, but the domain name doesn't have DNS records enabling a message to be directed back in response, the message can be rejected.
This setting is configured on the SMTP Service, Abuse tab:
Verify Return-Path has valid MX or A record
If this is checked, Mailtraq will lookup the MX and A records of the domain specified in the FROM: statement (which is the message's Return-Path). If Mailtraq cannot resolve this name, it will refuse the message. This is both because it cannot discharge its responsibilities, and because the message has probably been sent as part of an attack or is SPAM.
In the DNS Servers Field enter a list of Domain Name Servers that Mailtraq can use when resolving the MX records.
Click on Exceptions to edit the list of sender addresses that can bypass this check.