If your outgoing mail keeps landing in spam folders or getting bounced outright, a broken reverse DNS lookup is one of the most common culprits. This guide explains what reverse DNS is, why mail servers check it, and what to do if yours isn't set up correctly.
What is reverse DNS?
Most people are familiar with regular DNS: it translates a domain name (like avalonhosting.services) into an IP address so browsers and mail servers know where to connect. Reverse DNS does the opposite — it takes an IP address and looks up the domain name associated with it, using a special DNS entry called a PTR (pointer) record.
When another mail server receives an email from your mail server, it can perform a reverse DNS lookup on your server's IP address to see what hostname comes back. If the result looks legitimate and consistent with your sending domain, that's one more signal the receiving server uses to trust your mail. If the lookup fails or returns nothing, that's treated as a red flag.
Why reverse DNS matters for email delivery
Large mailbox providers such as Gmail, Microsoft 365, and Yahoo routinely check reverse DNS as part of deciding whether to accept, flag, or reject a message. A missing or broken PTR record won't necessarily block every email, but it consistently lowers sender trust and increases the odds of messages being marked as spam or refused outright.
Common reasons reverse DNS lookups fail
- No PTR record exists for the sending IP address, so the lookup returns nothing.
- The PTR record doesn't match the hostname the mail server actually presents when it connects (a mismatch between forward and reverse DNS).
- The mail server is using a dynamic or residential IP address, which typically has no PTR record and isn't meant for sending mail directly.
- The sending IP is on a spam blocklist — this isn't a reverse DNS issue technically, but it produces similar symptoms and is worth checking at the same time.
An important distinction for Avalon customers
Unlike an SPF or DKIM record, which you manage yourself in your domain's DNS zone, a PTR record is tied to the IP address itself and is controlled by whoever owns that IP block — in most cases, your hosting or network provider, not your domain registrar. This means you generally cannot create or edit a PTR record through your own domain's DNS settings.
If you send email through Avalon Hosting's mail servers and suspect a reverse DNS mismatch is affecting deliverability, the fix isn't something to attempt in your domain's DNS zone. Instead, contact Avalon Hosting support with the details (the sending IP address, the domain you're sending from, and any bounce messages you've received) so our team can verify and correct the PTR record on our end.
How to check if reverse DNS is the problem
- Run a reverse DNS lookup using a public tool, or from a command line with
nslookup <your-mail-server-IP>(Windows/Linux) ordig -x <your-mail-server-IP>(Linux/macOS). - Compare the hostname returned against the domain name your mail server actually uses to identify itself. They should match, or at least be clearly associated with your organization.
- Check any bounce-back messages you've received — many include specific wording about a reverse DNS or PTR record failure.
Common issues
My PTR record is correct but I'm still landing in spam. Reverse DNS is only one of many deliverability factors. Sender reputation, blocklist status, and proper SPF/DKIM/DMARC configuration all play a role too — it's worth checking each of these rather than assuming reverse DNS is the only cause.
Can I set my own PTR record? Not on Avalon's shared mail infrastructure — this is managed by our network team to keep it consistent and accurate. If you're on a dedicated IP and have a specific hostname requirement, reach out to support and we can accommodate it.
