via forums.cpanel.net => original post link
The system uses an alternate HELO of “domain_name” when sending mail from the “domain_name” domain.
There is no reverse DNS configured for the IP address () that the system uses to send this domain’s outgoing email.
To fix this problem, contact your system administrator and request that they create the following PTR record at “ns1.digitalocean.com”, “ns2.digitalocean.com”, and “ns3.digitalocean.com”: