What is reverse DNS used for?

Reverse DNS resolves an IP address to a hostname using a PTR record. It is used by spam filters, mail servers, and abuse trackers to verify that the IP sending email has a legitimate hostname associated with it. Missing or generic PTR records are a common cause of spam folder placement.

Does a PTR record affect email deliverability?

Yes. Most spam filters check PTR records as part of reputation scoring. A missing PTR record can increase your spam score by 1 to 3 points and cause delivery failures or spam placement at major mailbox providers.

How do I set up a PTR record for my mail server?

PTR records are controlled by the IP address owner, not the domain owner. Contact your hosting provider or ISP and request a PTR record pointing to your mail server hostname. Most VPS providers like DigitalOcean, Vultr, and Linode let you set reverse DNS directly in their control panels.

Reverse DNS Lookup

Q: How long does it take for a PTR record to propagate?

PTR records typically propagate within minutes to an hour. In some cases it can take up to 24 hours depending on your hosting provider and the DNS TTL configured.

Q: What should my PTR record point to?

Your PTR record should point to your mail server hostname, such as mail.yourdomain.com. The hostname should also resolve back to the same IP address. This is called forward-confirmed reverse DNS (FCrDNS) and is a strong signal of legitimate sending infrastructure.

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Look up the PTR record for any IP address. Instantly see the hostname your IP resolves to - used for mail server reputation, spam filter checks, and blacklist diagnostics.

What is reverse DNS?

Reverse DNS (rDNS) resolves an IP address to a hostname. Where regular DNS maps a domain name to an IP, reverse DNS does the opposite - it answers "what is the hostname for this IP?" The record type used is called a PTR record (pointer record) and is stored in the in-addr.arpa DNS zone for IPv4.

For email, the reverse DNS of your mail server's sending IP is one of the first things spam filters check. A missing or mismatched PTR record is a common cause of email delivery failures and spam folder placement.

Why reverse DNS matters for email deliverability

Most spam filters check PTR records. If your sending IP has no PTR record, many receiving servers will score your mail down or reject it outright.
PTR should match the forward DNS. The best practice is for IP → PTR hostname → A record → same IP. This is called forward-confirmed reverse DNS (FCrDNS) and is a strong signal of legitimate mail infrastructure.
Some ISPs require PTR records. Gmail, Outlook, and Yahoo all note missing or mismatched PTR records as a negative reputation signal.
PTR mismatch can trigger blacklisting. IPs with generic PTR records (like 123-45-67-89.dynamic.isp.net) are often treated as residential IPs and scored as potential spam sources.

How to set up reverse DNS for your mail server

PTR records are controlled by the owner of the IP address, not the domain owner. This means you need to contact your hosting provider or ISP to set reverse DNS for your sending IP.

VPS / cloud hosting (AWS, DigitalOcean, Linode, Vultr): Most have a reverse DNS setting in the control panel or network settings for each server. Set it to your mail server's hostname.
Dedicated servers: Contact your provider's support. They control the PTR record for your IP block.
Shared hosting: You usually cannot set reverse DNS on shared IPs. This is one reason dedicated sending IPs matter for bulk email.
Third-party senders (SendGrid, Mailgun, Amazon SES): They handle PTR records for their IP pools. If using a dedicated IP, they provide instructions for setting it up.

What to do if your PTR record is missing

Identify the IP your mail server uses to send email (visible in email headers as the server's IP).
Contact your hosting provider or ISP and request a PTR record pointing to your mail server's hostname.
Make sure the hostname resolves back to the same IP (forward-confirmed DNS).
Use this tool to verify the PTR record is correctly published after the change.
Check your domain's full email authentication with the InboxGreen domain checker.

FAQ

How long does it take for a PTR record to propagate?

PTR records typically propagate within a few minutes to an hour, but can take up to 24 hours in some cases depending on the ISP and DNS TTL settings.

Does a PTR record affect my spam score directly?

Yes. SpamAssassin, Postfix, and most enterprise mail filters check PTR records. A missing PTR can add 1-3 points to your spam score, which can push borderline mail into the spam folder.

My PTR record exists but emails still go to spam - what now?

PTR is just one factor. Check SPF, DKIM, DMARC alignment, IP blacklist status, and sending reputation using the InboxGreen full domain check.

What should my PTR record point to?

It should point to your mail server's actual hostname - typically something like mail.yourdomain.com or smtp.yourdomain.com. Avoid generic hostnames and make sure the hostname also resolves back to the same IP.