What is Reverse DNS?
Reverse DNS (rDNS) associates a given IP address with a specific domain. Reverse DNS is used to authenticate an address with the domain, as only the ISP or Internet connectivity provider can do this
For example, it might turn 220.127.116.11 (IP address) into example.mysite.com (hostname / domain name). rDNS does this by looking at the PTR record of the IP address in question and resolving it to a hostname based on the settings configured by a mail administrator.
You may use this 'test' to reduce spam by rejecting messages that do not have a valid Reverse DNS entry.
The setting is configured on the SMTP Service, Blacklists-tab.
From the Mailtraq Console, choose Options, Services, then the SMTP service, click Properties, and the Blacklists-tab, then click the [Explicit Black Lists] button, to access the IP Addresses-tab shown above.
Where can I find out more?
There are easy to follow articles about this topic in the Knowledgebase and at Wikipedia
Mailtraq's default settings are set to the optimum for being generally accepting of messages. Administrators should apply any additional controls with care to avoid rejecting too many legitimate messages.
It is an unfortunate fact that many legitimate mail servers are not correctly configured - applying tests to messages that require correct configuration may lead to rejecting messages you would otherwise wish to receive.
To avoid rejecting local users - copy your LAN definition into the SMTP White List.