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550 5.7.25: The sending IP address doesn't have a PTR record

A PTR record (reverse DNS) turns an IP address back into a host name. Gmail requires every sending IP to have one, and the host name must point back to the same IP.

Fix your sending setup Sending server has no reverse DNS

The sending IP has no reverse DNS.

  • Sent by: Gmail / Google Workspace
  • Permanent (hard bounce). Sending the same message again fails again.

How Gmail words it (source):

This message was blocked because the sending IP address doesn't have a PTR record, or the forwarding DNS entry doesn't reference the sending IP address.

Why it happens

  • You run your own mail server on a cloud or home IP with no reverse DNS.
  • The PTR record exists, but its host name resolves to a different IP.
  • Mail is sent over IPv6 and only the IPv4 address has a PTR record.

What to do

  1. Ask whoever owns the IP (your hosting or internet provider) to set the PTR record to your mail server's host name. You cannot set it in your own domain's DNS.
  2. Make that host name resolve back to the same IP.
  3. If IPv6 is the problem, add a PTR for the IPv6 address or send over IPv4.
  4. If you use an email service and see this, send them the bounce: the IP is theirs.

Don't confuse it with

421 4.7.0 and 451 4.7.23 with "PTR record" in the text are the same problem as a temporary slowdown. Microsoft uses 550 5.7.25 for IPv6 senders without reverse DNS.

Questions

Is the recipient's address wrong?

No. The problem is the server that sent the email.

Is a PTR record the same as SPF?

No. SPF is set by the domain owner and lists allowed servers. A PTR record is set by the owner of the IP address.

Got a different bounce?

Paste the whole message into the bounce code lookup. It reads the code and the words and tells you whose move it is.

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