Hurricane MTA Server gives you an option to set a host name when configuring the IP settings. This host name is a very important setting that should not be overlooked. The value specified here will be sent to the recipients' mail server using the HELO/EHLO command during the SMTP connection. At this point the remote server will then do a reverse DNS (PTR) record lookup on the IP you are connecting from and attempt to match the two values. If they do not match, many mail servers will give the message SPAM points or totally reject the message. To prevent this from happening you must make sure that your DNS is set up correctly for the IP address(es) you select for outbound delivery.
The forward DNS entry for the host name you choose should point to the IP address while the PTR record or reverse DNS entry for the IP must point to the host name.
For example, in Hurricane MTA Server if you have the below IP set up.
IP Host Name
The following must be the case.
mail.mydomain.com -> Must Resolve to -> 18.104.22.168
22.214.171.124 -> Must Resolve To -> mail.mydomain.com