550 5.7.25: Sending IP has no reverse DNS (PTR) record
Gmail returns 5.7.25 when the sending IP has no PTR (reverse DNS) record, or the hostname it points to does not resolve back to that IP. The temporary form is 451 4.7.23. Only whoever controls the IP can set PTR: your hosting provider or the mail service you send through.
The exact messages
Gmail / Google Workspace
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 / Google Workspace
451 4.7.23 The sending IP address for this message doesn't have a PTR record, or the PTR record's forward DNS entry doesn't match the sending IP address.
Microsoft 365 / Exchange Online
5.7.25 Access denied, the sending IPv6 address [2a01:111:f200:2004::240] must have a reverse DNS record
Why it happens
- Mail is sent straight from a VPS or home server whose IP has no PTR record.
- The PTR record points to a hostname whose A or AAAA record does not point back to the same IP.
- The server started sending over IPv6, and the IPv6 address has no reverse DNS.
How to fix it
- Set a PTR record for the sending IP in your hosting provider’s control panel (for example mail.yourdomain.com).
- Create a matching A (or AAAA) record so the forward and reverse lookups agree.
- If you cannot set PTR on IPv6, force the mail server to send over IPv4.
If you send cold email
This mostly hits self-hosted senders. If you send through Google Workspace or Microsoft 365 mailboxes, their IPs already have PTR records, and seeing this code means something is relaying mail outside them.
How WarmHawk handles it
WarmHawk checks SPF, DKIM and DMARC for each sending domain against live DNS and keeps "could not check" separate from "failed", so a flaky resolver never looks like a broken record. New mailboxes warm up by sending to partner inboxes and recording where each email landed, so an authentication problem shows up in the warmup results before the mailbox graduates to campaigns. How WarmHawk works →
Check your domain now
These free checkers read your live DNS: no account, up to 15 domains at once.
Related bounce codes
- 4.7.0Temporarily deferred: low reputation, PTR or TLS
- 5.7.26Unauthenticated sender (no SPF or DKIM pass)
Sources, checked 2026-09-29: Google Workspace: Gmail SMTP errors and codes · Microsoft Learn: NDRs and SMTP errors in Exchange Online. Have a different bounce? Paste it into the decoder →
Questions
5.7.25 questions
What does 5.7.25 mean?+
Gmail returns 5.7.25 when the sending IP has no PTR (reverse DNS) record, or the hostname it points to does not resolve back to that IP. The temporary form is 451 4.7.23. Only whoever controls the IP can set PTR: your hosting provider or the mail service you send through.
Is 5.7.25 a temporary or permanent error?+
Both forms exist. A reply starting with 4 (such as 4.7.23) is temporary, and the sending server will retry; a reply starting with 5 is permanent, and the message will not be retried until you fix the cause.
How do I fix 5.7.25?+
Set a PTR record for the sending IP in your hosting provider’s control panel (for example mail.yourdomain.com). Create a matching A (or AAAA) record so the forward and reverse lookups agree. If you cannot set PTR on IPv6, force the mail server to send over IPv4.