SMTP enhanced status code 5.7.25

What the registry says

The basic codes it travels with

• 550 Requested action not taken: mailbox unavailable (e.g., mailbox not found, no access, or command rejected for policy reasons)

In practice

Gmail requires a PTR record for every sending IP and returns 550 5.7.25 if it is missing or does not match. Microsoft returns 5.7.25 for IPv6 senders without reverse DNS. If you use a sending service, it manages PTR records for you. On your own server, set the PTR through your hosting provider.

What the sender should do

Set a PTR record for the sending IP that resolves forward to the same address. On shared services, the provider controls this.

How providers use X.7.25

Quoted from each provider’s own error reference.

• Gmail 550 5.7.25

  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. Gmail requires that sending IP addresses have a PTR record. Learn more about requirements for sending IP addresses. To learn more about Gmail requirements for bulk email senders, visit Email sender guidelines.

• Microsoft 365 5.7.25

  Access denied, the sending IPv6 address [2a01:111:f200:2004::240] must have a reverse DNS record

Common questions

What does 5.7.25 mean?

X.7.25 means the sending IP failed a reverse DNS check: it has no PTR record, or the PTR name does not resolve back to the same IP.

What should I do about 5.7.25?

Set a PTR record for the sending IP that resolves forward to the same address. On shared services, the provider controls this.

Would an email verifier have caught 5.7.25?

No. This reply is about your sending setup, the message or the receiving system, not about whether the address exists, so verifying the list will not prevent it.

Full guides for this code

• 550 5.7.25 — no PTR record for sending IP (Gmail)