Trend Micro Email Security adds a layer of protection by validating the reverse DNS (rDNS) records for inbound email messages.
With the reverse DNS validation feature, an administrator can configure the following:
Validation settings: whether to reject an email message when the corresponding PTR record is missing or invalid
Block list: a list of PTR domains for message blocking
During the SMTP connection setup stage, Trend Micro Email Security uses the email sending IP address to perform rDNS lookup. If the query result matches the criteria in any rDNS validation settings or the PTR domain block list, Trend Micro Email Security rejects the email message before the message body is sent over.
If the IP address sending an email message matches the Approved IP address list of IP reputation, the email message bypasses revere DNS validation.