Mailwarm Email Warmup

Reverse DNS Lookup

Run a free reverse DNS lookup to find the PTR record for any IP address and check that it points back to the same IP, the setup mail servers expect.

Examples:

Why reverse DNS matters for email deliverability

When your server connects to deliver an email, the receiving server looks up the PTR record of your IP. If there isn't one, or the hostname it returns doesn't resolve back to the same IP, your server looks like a compromised machine or a home connection, and mail is often rejected or sent to spam.

  • Missing PTR: the IP has no hostname at all. Common on new VPS and cloud servers until you set it.
  • Not forward-confirmed: the PTR hostname doesn't resolve back to the IP, so the identity can't be verified.
  • Mismatch with HELO: the name your server announces in its SMTP greeting differs from its PTR hostname. Many filters score this as suspicious.
  • Generic hostnames: names like 203-0-113-10.dynamic.isp.net look like residential IPs and are blocked by many lists.

If you send through Google Workspace, Microsoft 365 or an ESP, they manage reverse DNS for you. It matters most for your own SMTP server or a dedicated IP, together with SMTP warmup and a clean blacklist check.

Reverse DNS Lookup: Common Questions

Everything you need to know about PTR records

A reverse DNS lookup turns an IP address into a hostname by querying its PTR record. It is the opposite of a normal DNS lookup, which turns a hostname into an IP. Mail servers use it to check that the server connecting to them has a real, properly configured identity rather than an anonymous address.

Enter an IP address in the reverse DNS lookup above to see its PTR record and whether that hostname resolves back to the same IP. You can also enter a domain to check its mail servers. From a terminal, use dig -x followed by the IP on macOS and Linux, or nslookup followed by the IP on Windows.

Open Command Prompt or PowerShell and type nslookup followed by the IP address, for example nslookup 8.8.8.8, then press Enter. Windows queries the PTR record and shows the hostname next to Name. In PowerShell you can also run Resolve-DnsName with the IP address to get the same result in more detail.

Reverse DNS matters because mailbox providers use it to judge whether a sending server is legitimate. Gmail and Yahoo require valid forward and reverse DNS for sending IPs, and many servers reject or spam-folder mail from IPs without a PTR record. The PTR hostname should resolve back to the IP and match the HELO name.

You set up a PTR record through whoever owns the IP address, not your normal DNS provider. On a VPS or cloud server, look for a reverse DNS setting in your hosting dashboard. For other IPs, ask your hosting provider or ISP. Point it to a hostname whose A record resolves back to the same IP.

Reverse DNS is the foundation

Once your server is set up correctly, Mailwarm builds the reputation that gets its email into the inbox, with automated warmup, a deliverability audit and an account manager for every customer.

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