Most people who work with websites are familiar with the basic DNS lookup: you type a domain name, DNS returns an IP address, and your browser connects to the right server. That is a forward DNS lookup. Reverse DNS works in the opposite direction - it looks up an IP address and returns a hostname - and it plays a surprisingly important role in email deliverability.
Forward vs. Reverse DNS
In standard (forward) DNS, an A record maps a hostname to an IP address. For example:
mail.yourbusiness.ca→198.51.100.42
In reverse DNS, a PTR record (short for Pointer record) maps an IP address back to a hostname. For example:
198.51.100.42→mail.yourbusiness.ca
The forward and reverse records are stored differently. Forward DNS records live in your domain's DNS zone, managed by your registrar or DNS provider. Reverse DNS records live in a special zone managed by the owner of the IP address block - which is typically your internet service provider or hosting company, not you.
This distinction matters a great deal when it comes to getting your PTR record set up correctly.
Why Mail Servers Check Reverse DNS
When a mail server at Gmail, Microsoft 365, Bell, or Rogers receives an incoming email, it performs a series of checks to assess whether the sending server is legitimate. One of the first and most fundamental checks is reverse DNS.
The receiving server takes the IP address that connected to it and performs a PTR lookup. It then checks whether the hostname returned by that PTR lookup matches the hostname the sending server announced in its SMTP greeting (the HELO/EHLO command). If these do not match - or if no PTR record exists at all - the receiving server treats this as a signal of potential spam or fraud.
The consequences vary by receiving mail server. Some servers reject the connection outright with a 550 error. Others accept the message but assign it a higher spam score that pushes it to junk. Others log it as suspicious. In any case, missing or incorrect reverse DNS is a deliverability liability.
What Happens When It Is Missing or Mismatched
A missing PTR record means the reverse DNS lookup returns no result. From a receiving mail server's perspective, this is a red flag - legitimate mail servers have PTR records.
A mismatched PTR record means the lookup returns a hostname that does not match what the sending server claimed. This is also suspicious and will affect spam scoring.
Both conditions are relatively common in practice, particularly on shared hosting where many domains share a single IP address and the hosting provider has not configured reverse DNS appropriately for email use.
Who Controls It - and How to Fix It
Because PTR records are managed by the IP owner (your hosting provider), you cannot set them yourself through your domain registrar or DNS control panel. You have to request the change from the company that owns the IP address your mail is sent from.
For shared hosting customers, this means contacting your hosting provider's support team and requesting that a PTR record be configured for the sending IP. Provide them with the exact hostname you want the PTR record to resolve to - this should match your mail server's hostname and your SMTP greeting.
If you are on a VPS or dedicated server, your hosting provider can usually set PTR records through a control panel or on request. Many VPS providers have a reverse DNS field right in their server management interface.
When This Matters for Shared Hosting vs. VPS
On shared hosting, many domains share the same outgoing mail server IP address. The PTR record for that IP is set by the hosting provider and typically resolves to the hosting provider's own hostname (such as mail.yourhostingcompany.com). This is usually acceptable for basic deliverability, as long as the hosting provider maintains a good IP reputation.
The issue arises when you are sending significant email volume, doing cold outreach, or using that shared IP for a custom mail setup. If the shared IP has been flagged for spam by previous tenants, you inherit that reputation.
On a VPS or dedicated server, you have your own IP address and therefore full control (via your provider) over the PTR record. This is one of the reasons businesses that take email seriously - especially for outbound marketing or transactional email - eventually move to a dedicated IP with a clean PTR record.
Quick Checklist for Email Deliverability
Reverse DNS is one component of email deliverability. A complete check should also include:
- SPF record - authorizes which servers can send email for your domain
- DKIM - cryptographically signs your outgoing messages
- DMARC - policy record that tells receivers what to do with unauthorized mail
- PTR record - the subject of this article, matching your sending IP to your hostname
Tools like MXToolbox and mail-tester.com can run a comprehensive deliverability check and flag any issues with your PTR record alongside SPF, DKIM, and DMARC configuration.
