PTR record
The name an address reverses to. Lives in the in-addr.arpa zone and is controlled by whoever holds the address range — normally the hosting provider, not the domain owner.
Reverse DNS maps an address back to a name. Anyone who controls an address range can point that name anywhere, so receiving mail servers check the round trip: the name must resolve back to the same address. That is forward-confirmed reverse DNS, and it is what actually matters.
The name an address reverses to. Lives in the in-addr.arpa zone and is controlled by whoever holds the address range — normally the hosting provider, not the domain owner.
The PTR name resolves back to the same address. Both directions agree, which is the check receiving mail servers perform.
An address with no PTR, or one where the two directions disagree, is a strong signal of a compromised host or a bulk sender. Many servers refuse such mail outright; most of the rest penalise it heavily.
Only the holder of the address range. If you rent a server, that is your provider — and the request is routine, usually a field in their control panel.
A correct setup needs both halves. The provider sets a PTR record on the address, pointing at a name you control — mail.example.com, typically. You then publish an A record for that name pointing back at the same address.
Miss the second half and the check fails even though the PTR looks right in every lookup tool that only shows one direction. This is the most common way a mail server ends up quietly penalised: the PTR is there, everyone can see it, and the round trip does not close.
The name should also match what the server announces in its SMTP HELO. Receivers that compare the two treat a mismatch as another weak signal, and the three together — PTR, forward record, HELO — are what make a sending address look legitimate rather than merely configured.
Only if you control the address range, which for a rented server means the hosting provider. It is a routine request and often self-service in a control panel. The forward A record is yours to publish, and both are needed.
Almost always the forward half is missing. The PTR points at a name, but that name has no A record pointing back at the address — so the round trip does not close. Publish an A record for the PTR name and re-check.
A little. Some logging and monitoring resolves addresses to names for readability, and a few services use it as a weak signal. But mail is where the absence of it has real consequences.
Every server that sends mail, without question. For others it is tidy rather than necessary. An address that will never originate SMTP loses nothing by having no PTR record.
It is allowed, though uncommon and generally discouraged. Receivers differ in how they handle it, and the ambiguity is one more thing that can go against you. One name per address is the safe arrangement.
A record changed by someone who left, a registrar nobody has the login for, a zone signed but never delegated. We take over the operation of this properly — documented, monitored, and changed through a process rather than through whoever is awake.