Reverse DNS lookup
The hostname an IP address claims, and whether that claim checks out.
Why this matters
Receiving mail servers check that a sending address has a reverse record, and that the name it gives resolves back to the same address. A missing or mismatched record is a common reason legitimate mail is treated as spam.
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Perguntas frequentes
What is a PTR record?
The record that maps an address back to a name. It lives in a special zone: to find the name for 8.8.8.8 a resolver looks up 8.8.8.8.in-addr.arpa, with the address reversed. Only whoever controls the address block can set it, which is why you ask your hosting provider rather than your DNS host.
What is forward-confirmed reverse DNS?
Checking both directions. The address gives a name, and that name must give the address back. It proves the two are under common control, which is why mail servers use it as a cheap sign of legitimacy. A reverse record alone is easy to set to anything; a matching pair is not.
My mail is being rejected for missing reverse DNS
Ask whoever owns the IP address — your hosting provider or ISP — to set a PTR record for it, pointing at your mail server’s name. Then make sure that name has an A record pointing back at the same address. Both halves are needed; one without the other usually does not help.