How to Check the Reverse DNS (PTR) of Many Domains' MX Servers

To check the reverse DNS of a domain's mail servers, find its MX hosts, resolve each to an IP, read the IP's PTR record and test that the PTR name resolves back to the same IP. The bulk MX reverse DNS checker does this for up to 100 domains a run, 500 after a free Google sign-in. No connection is made to the mail servers.

What reverse DNS is for a mail server

Forward DNS turns a hostname into an IP. Reverse DNS does the opposite: the IP's PTR record, stored under in-addr.arpa, names a host. Receiving servers often look up the PTR of a connecting IP, and many treat an IP with no PTR, or one that does not resolve back to it, as a sign of a badly run sender. RFC 1912 recommends that every IP with a hostname has a matching PTR. Forward-confirmed reverse DNS (FCrDNS) is the stronger test, and the one this tool runs.

Doing it by hand

dig +short MX example.com
dig +short A mx1.example.com
dig +short -x 203.0.113.10
dig +short A mail-server-7.example.net

Take the MX host, resolve it to an IP, read the PTR of that IP, then resolve the PTR name and check you get the same IP back. Repeat for every domain and every host.

Step 1: paste the domains

Paste domains, email addresses or URLs, one per line, up to 100 a run or 500 after a free Google sign-in.

Step 2: run the check

The three lowest-priority MX hosts of each domain are resolved to an IPv4 address, and each address's PTR is read and confirmed, 5 domains a request. Up to five PTR names per address are forward-checked. Private and reserved addresses are skipped, and IPv6 is not covered.

Step 3: read each row

Result	What it means
PTR matches MX host	The tidy case
Forward-confirmed	A valid PTR under a different name, as hosted providers often have
PTR not confirmed	A PTR exists but its name does not resolve back to the IP
No PTR record	The IP has no reverse record
No MX to check	The domain has no MX records
Lookup failed	DNS did not answer properly

Does an MX server's PTR need to match its MX name

Not by any rule for receiving mail. An MX host receives connections; the PTR check matters most for servers that connect out. It becomes relevant when the same machines also send your mail, which is typical for a self-hosted server and uncommon behind a large hosted provider. So PTR not confirmed and No PTR record are worth a look if the server also sends mail.

Fixing a missing or wrong PTR

A PTR belongs to whoever owns the IP address block, usually the hosting provider, so you change it in their control panel or by asking them, not in your domain's DNS. Our guide to reverse DNS and PTR records for email covers how to ask, and the Spamhaus HELO and PTR requirement covers why it matters. To check a list of sending IPs rather than MX hosts, use the bulk reverse DNS lookup.

What this check cannot do

• It checks DNS only. It does not connect to the mail servers or read their HELO name.
• Only IPv4, and the first address of each of the three lowest-priority MX hosts.
• A missing PTR on a hosted provider's shared MX name is common and not a fault of the domain.
• The limit is 100 domains a run without an account and 500 signed in.

Check the addresses you send to

Correct DNS gets mail to the door; the address still has to exist. Upload your list on the verify page: the first 100 email checks are free with a Google sign-in, no card. Each address comes back valid, risky or invalid with a reason, and nothing is sent to anyone on the list. For larger or recurring lists, see bulk email verification, list cleaning and pricing.

Check your domains now

Paste them into the bulk MX reverse DNS checker.