550 5.7.25 PTR record required Email / SMTP Origin: Network Last updated 4 Nov 2026

SMTP: 550-5.7.25 The IP address sending this message does not have a PTR record setup, or the corresponding forward DNS entry does not point to the sending IP

Gmail (and others) require your sending IP to have a reverse DNS (PTR) record that resolves back to the same IP; yours has none or it does not match.

Exact message you may see 550-5.7.25 The IP address sending this message does not have a PTR recordPTR record requireddoes not have a PTR record setup550 5.7.25 PTR recordreverse DNS lookup failed
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Seen on: SMTP Linux

Meaning

A PTR record maps the IP to a hostname; the hostname's A record must map back to the same IP (forward-confirmed reverse DNS). Only the owner of the IP block (hosting provider/ISP) can set the PTR. Use a hostname that matches your HELO/EHLO name.

Common causes

  • No PTR record for the sending IP
  • PTR exists but its hostname's A record points elsewhere
  • Generic ISP PTR (e.g. 203-0-113-5.isp.net)
  • HELO name differs from the PTR
  • Sending from a cloud IP without configuring rDNS

⚡ Quick fix

  1. Ask your host to set the PTR to mail.example.com
  2. Create the matching A record for the same IP
  3. Set Postfix myhostname = mail.example.com so HELO matches

Detailed fix by platform

Linux

  1. dig -x 203.0.113.5 +short then dig +short mail.example.com — both must agree

Postfix

  1. postconf -e 'myhostname = mail.example.com'; postfix reload

How to diagnose

  1. PTR — Does dig -x IP return a name?
  2. Forward — Does the name resolve back to the IP?
  3. HELO — Same as PTR?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: Network. Errors that are often confused with or caused by this one (click to open):

421 4.7.0 Try again later (rate limited) — SMTP: 421 4.7.0 Our system has detected an unusual rate of unsolicited mail originating from your IP address. Mail sent from your IP address has been temporarily rate limited (Email / SMTP)421 4.7.0 Try again l…550 5.7.1 Blocked using zen.spamhaus.org — SMTP: 550 5.7.1 Service unavailable; Client host [203.0.113.5] blocked using zen.spamhaus.org (Email / SMTP)550 5.7.1 Blocked usi…550 5.7.26 — 550 5.7.26 This mail has been blocked because the sender is unauthenticated (SPF/DKIM/DMARC) (Email / SMTP)550 5.7.26554 5.7.1 Service unavailable; client host rejected — SMTP: 554 5.7.1 Service unavailable; Client host [203.0.113.5] blocked / 554 5.7.1 <mail.example.com>: Client host rejected: Access denied (Email / SMTP)554 5.7.1 Service una…cURL error 6 — cURL error 6: Could not resolve host: api.example.com (PHP)cURL error 6DKIM: no key for signature — DKIM: dkim=permerror (no key for signature) / key not found in DNS selector._domainkey (Email / SMTP)DKIM: no key for sign…DMARC: no record found — DMARC: dmarc=none (no DMARC record found for example.com) — bulk sender requirements not met (Email / SMTP)DMARC: no record foundHelo command rejected: need fully-qualified hostname — SMTP: 504 5.5.2 <localhost>: Helo command rejected: need fully-qualified hostname (Email / SMTP)Helo command rejected…550 5.7.2…

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