How to Find Which Sending IPs Have No Reverse DNS (Before You Send)

Paste your sending IPs into the bulk reverse DNS lookup and filter to the rows with no PTR or no forward match. Gmail checks that every sending IP has a PTR record and that the hostname in it resolves back to the same IP. An IP that fails either check is the one to fix before you send from it.

Check reverse DNS for a list of IPs →

Check them in bulk

1. Open the bulk reverse DNS lookup.
2. Paste the IPs, one per line: up to 100 a run, or 500 after a free Google sign-in. IPv4 and IPv6 both work, and so do lines copied from a log or a Received header: the first IP on each line is used.
3. Press Look up PTR records.
4. Read each row: the PTR hostname, Confirmed when it resolves back to the same IP, and Generic when it looks like an auto-generated pool name.
5. Filter to IPs with no PTR or no forward match, and download the CSV.

Do it by hand

printf "142.251.189.27\n140.82.112.3\n104.16.132.229\n8.8.8.8\n" > ips.txt

while read -r ip; do
  ptr=$(dig +short -x "$ip" | head -1)
  if [ -z "$ptr" ]; then echo "$ip,NO PTR"; continue; fi
  if dig +short a "$ptr" | grep -qx "$ip"; then echo "$ip,$ptr,confirmed"; else echo "$ip,$ptr,not confirmed"; fi
done < ips.txt
# 142.251.189.27,yucbfcd-in-f27.1e100.net.,confirmed
# 140.82.112.3,lb-140-82-112-3-iad.github.com.,confirmed
# 104.16.132.229,NO PTR
# 8.8.8.8,dns.google.,confirmed

We ran this on 9 November 2026. dig -x turns the IP into its reverse name for you: 104.16.132.229 becomes 229.132.16.104.in-addr.arpa, the scheme RFC 1035, section 3.5 defines. For 104.16.132.229, a Cloudflare web address, the answer was status: NXDOMAIN: no PTR exists. That's normal for a web server and a problem for a mail server.

The loop checks IPv4 forward records only. For IPv6 sending IPs, swap dig +short a for dig +short aaaa.

Why it matters, and what to do with each result

Google's sender guidelines say a sending server's public IP "must have a corresponding PTR record that resolves to a hostname", and that "the sending IP address must match the IP address of the hostname specified in the Pointer (PTR) record."

• No PTR. Set one before sending from that IP. Most VPS and dedicated server hosts have a reverse DNS field in their control panel; otherwise ask their support.
• PTR but not confirmed. Add an A (or AAAA) record for the hostname in your own DNS, pointing at the IP. This part you do control.
• Generic name such as 203-0-113-7.dynamic.example.net. Change it to a name under your own domain, like mail1.yourdomain.com, which matches your HELO name.
• Confirmed. Nothing to do. Make sure your server's HELO uses the same name; see Spamhaus's HELO and PTR requirement.

For what a PTR record is and who can change it, see reverse DNS (PTR) records for email. To see which network each IP belongs to, use the bulk IP to ASN lookup.

Next step: check the list you'll send to

Clean reverse DNS gets your server's connection accepted. Bounces from dead addresses still hurt the same IPs' reputation. Upload the list at /verify to check every mailbox without sending. The first 100 checks are free with a Google sign-in, no card.

Pro, $39 a month: Unlimited email verification.* Never metered, never cut off. See pricing.

*Fair use: the first 100,000 checks a month at full speed, then slower, never cut off.

More: IPv6 email sending requirements, find who owns the IPs in a bounce or email header.