Reverse DNS (PTR) Lookup

What the Reverse DNS Lookup checks

Receiving mail servers look at the IP address that connected to them and ask DNS for its name. This tool runs the same checks:

• PTR record. Does the address have a reverse DNS name?
• Forward confirmation (FCrDNS). Does that name have an A record (or AAAA for IPv6) that points back to the same address?
• Generic name (heuristic). Does the name look like an auto-generated one, such as 203-0-113-10.dyn.example.net?

Enter an IPv4 or IPv6 address, or a domain. For a domain we look up its MX records and check up to four mail server addresses. Private and reserved addresses are refused.

How to read the results

• Pass. A PTR exists, and its name resolves back to the address.
• Warning. The name looks generic. Some receivers score that as a likely consumer or unmanaged host.
• Fail. There is no PTR, or the name doesn't resolve back to the address.
• Not tested. A lookup timed out. Try again.

Why reverse DNS matters for email

Google's email sender guidelines say that all senders must have valid forward and reverse DNS for their sending IPs, and that the public IP of a sending server must have a PTR record that resolves to a host name. Many other receivers reject or score down mail from addresses with no PTR, or with a PTR that doesn't match.

The PTR name doesn't have to be in the same domain as your From address. It should be a stable name for the server, such as mail.yourcompany.com or your mail provider's own host name, and it should match the name the server uses in its SMTP greeting.

Common problems and fixes

No PTR record. Open a ticket with your hosting provider or ISP, or use the reverse DNS setting in your cloud console. You can't add a PTR in your own domain's DNS zone.

PTR doesn't resolve back. If the PTR is mail.yourcompany.com, add an A record for mail.yourcompany.com pointing to the same IP. Or change the PTR to a name that already does.

Generic name. Ask the provider to replace the default name with your mail server's name, then add the matching A record.

You use Microsoft 365 or Google Workspace. Their sending servers already have correct reverse DNS. You only need to manage PTR records for servers you run yourself, such as an on-premises Exchange server or a relay.

Limitations

• For a domain we check inbound mail servers from its MX records. The servers that send your mail may be different. Enter their IP addresses to check them directly.
• We check up to two PTR names per address.
• The generic-name check is a pattern match. A name like static-203-0-113-10.example.net may belong to a perfectly managed server.

Related

Check the same addresses against spam blocklists with the Blacklist Checker, or read the Gmail, Yahoo and Microsoft sender requirements.