InboxGrade

Reverse DNS (PTR) missing

Your sending IP has no reverse-DNS (PTR) record, or the record doesn't match your HELO/EHLO hostname.

Impact — Medium impact

No rDNS is the single strongest signal of 'this is not a legitimate mail server.' Major receivers (Gmail, Yahoo, Microsoft) heavily penalize or outright reject mail from IPs with no PTR.

What causes it

  1. You're on a VPS or cloud instance and never set the PTR record (requires provider cooperation).
  2. The PTR exists but points to a generic hostname like ec2-1-2-3-4.compute.amazonaws.com, which also looks residential/transient to receivers.
  3. The PTR exists but doesn't match the hostname your mail server HELOs with.

How to fix it

Step 1: Set PTR via your cloud/VPS provider

AWS: use EC2 reverse DNS request form. DigitalOcean: Networking → PTR Records. Linode: Network tab per Linode. Hetzner: Server detail page → Reverse DNS.

Step 2: PTR must A-resolve back to the same IP

Forward-confirmed reverse DNS: IP → PTR → hostname → A record → same IP. If this chain breaks anywhere, receivers reject.

Step 3: Match HELO/EHLO to PTR

Configure your mail server to HELO with the exact hostname its PTR points to. Mismatches trigger spam flags.

Fixed it? Run a fresh test to confirm.

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