PTR validation
The PTR record check perform a reverse query using the IP address of the host record.
Every address record (A and AAAA) have a corresponding PTR record. The PTR records reside under the ARPA TLD and are in most cases managed by other entities than the forward zones.
Many server systems on the Internet, especially Mail servers (MTA), use the reverse records (PTR) as part of the mechanisms to fight spam. The connecting server is identified with its IP address and provide its identify with its host name. The IP address are then used in the reverse query to check if the PTR record points back to the correct host name.
This check will validate that the PTR record for each IP address associated with the host resource records (A and AAAA) points back tho the correct name.
This check is automatically disabled for host CNAME records and host records resolving to private and reserved IP addresses.
Event severities and messages
WARNING
{IP} incorrectly points to {name}
Forward and reverse records don't match. This could affect the the ability to communicate with different Internet hosts.
ERROR
{IP} has no registered PTR record.
Every now and then this check come across arpa-zones where the responsible entity have failed to register reverse records. In most cases regarding the IPv4 part of the ARPA name space (in-addr.arpa) the domain owner (usually ISP's or similar) use generated PTR records as part of their registration requirement. But sometimes this fails. If possible reach out to your service provider and ask to have your PTR record registered.
UNKNOWN
PTR query for {IP} timed out.
The check could not be completed due to time out failure.
Solutions, tips & tricks
The PTR records and its ARPA zones are directly related to the IP address space. Organisations are usually assign one or more IP subnets from the ISP they use. The ISP's can and should upon request delegate the corresponding ARPA zone to the organisation for easier smoother zone management. Regardless if your organisation uses IPv4 and/or IPv6 the corresponding ARPA zones become much easier to manage if you host them yourself.
IPv4 and IPv6 addresses occupy different sub-trees in the ARPA domain name space.
The space under in-addr.arpa. is used for IP version 4, and
the space under ip6.arpa. is used for IP version 6.