Configure reverse DNS
Align PTR and HELO/EHLO for each sending IP before warmup or production volume.
- Difficulty:
- Intermediate
- Prerequisites:
- IP ownership or provider PTR support, Forward A/AAAA for HELO name
- Last updated:
- 2026-07-15
- Author:
- empire
Objective
Align reverse DNS and HELO
Publish consistent PTR and HELO/EHLO identity for sending IPs.
Starting state
Sending IP allocated; forward hostname chosen
Prerequisites
- IP ownership or provider PTR support
- Forward A/AAAA for HELO name
Estimated time
1–2 hours
Difficulty
intermediate
Required access
- DNS / IP provider portal
- MTA or ESP HELO settings
Inputs
- Sending IP
- Desired HELO hostname
Step-by-step instructions
- Choose the mail hostnamePick a stable FQDN that will serve as HELO/EHLO for this IP.
- Publish forward and reverse DNSEnsure A/AAAA exists for the hostname and PTR for the IP matches it.
- Set HELO and verifyConfigure the MTA/ESP HELO string and confirm reverse lookups from outside.
Verification
- dig -x IP returns the HELO hostname
- Outbound test shows matching HELO in receiver logs
Common mistakes
- PTR stuck on ISP defaults
- HELO uses bare IP literal
- Use provider-managed PTR vs self-managed reverse zone?
Rollback / recovery
- Revert HELO to prior known-good hostname if delivery regresses
Expected outcome
Each sending IP presents a consistent reverse DNS and HELO identity.
When to escalate
- Provider cannot publish PTR for the IP