PTR and Reverse DNS Setup for SMTP Servers

A PTR record maps an IP address back to a hostname. Gmail requires valid forward and reverse DNS for sending domains or IPs, and a clean SMTP identity normally keeps PTR, A record and HELO consistent.

1. Assign one deliberate mail hostname

Choose a stable hostname such as mail.example.com for each sending IP or route. Ask the IP provider to publish the PTR because reverse DNS is controlled by the owner of the IP block.

2. Create forward-confirmed reverse DNS

The IP PTR should return the mail hostname, and that hostname A record should return the same IP. This two-way check is commonly called forward-confirmed reverse DNS.

3. Align HELO with the route

Configure the SMTP server to introduce itself with the intended hostname. Avoid generic provider hostnames, bare IP literals or a HELO name that resolves to a different route.

4. Verify every IP independently

Multi-IP servers need a deliberate PTR and source/HELO mapping for each active sending IP. Recheck after migration, IP replacement or network changes and compare the result with a received-message header.

Implementation checklist

• PTR exists for every sending IP
• PTR hostname has matching A record
• HELO uses the intended hostname
• TLS certificate matches service hostname
• Received header shows expected route

Primary references

• Gmail Email sender guidelines
• Postmaster Tools dashboards