SMTP 550 5.7.25
no PTR record for sending IP (Gmail)
SMTP 550 5.7.25 means Gmail rejected the message because the sending IP has no PTR (reverse DNS) record, or the PTR does not match a forward DNS record. Google requires reverse DNS on every sending IP. The fix is on your sending server, not the recipient's.
Should you remove the address?
Keep the address; fix the sending side
Keep it. Reverse DNS is about your server.
Block. Retrying changes nothing until the cause on your side is fixed.
How it appears
550 5.7.25 This message was blocked because the sending IP address doesn't have a PTR record, or the forward DNS entry of the PTR record doesn't match the sending IP address.
What causes it
- The sending IP has no reverse DNS record at all.
- The PTR hostname does not resolve back to the same IP.
- Mail is going out from a new server or cloud IP that was never set up for sending.
How to fix it
In order — try the first one first.
- Ask whoever controls the IP (your host or ISP) to set a PTR record for it.
- Make sure the PTR hostname has an A record pointing back at the same IP.
- Use that hostname in your server's HELO or EHLO greeting.
- Do not suppress recipients. The rejection is about your IP.
Who sends it
Gmail, and Microsoft 365 for IPv6 senders.
Gmail
Reply text 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 also defers with 421 4.7.0 or 451 4.7.23 for the same problem.
Microsoft 365
Reply text Access denied, the sending IPv6 address <address> must have a reverse DNS record
Applies to mail Microsoft receives over IPv6.
Common questions
- What does SMTP 550 5.7.25 mean?
- SMTP 550 5.7.25 means Gmail rejected the message because the sending IP has no PTR (reverse DNS) record, or the PTR does not match a forward DNS record. Google requires reverse DNS on every sending IP. The fix is on your sending server, not the recipient's.
- Should I retry a 550 5.7.25 error?
- No. 550 is a permanent failure, so the message will never be delivered no matter how many times you try. Remove the address — repeated sends to permanent failures are one of the main signals mailbox providers use to throttle a sender.
- How do I fix SMTP 550 5.7.25?
- Ask whoever controls the IP (your host or ISP) to set a PTR record for it.
- Is 550 5.7.25 a hard bounce or a soft bounce?
- 550 5.7.25 is a block rather than a classic hard or soft bounce. The rejection is about your sending (authentication, reputation, content or the recipient's policy), not about whether the address exists. Retrying changes nothing until the cause on your side is fixed.
- Should I remove the address after a 550 5.7.25 bounce?
- Keep it. Reverse DNS is about your server.
- Will verifying my list prevent 550 5.7.25?
- Not directly. This code is about your authentication, IP or domain reputation, so verification will not lift it. A clean list still matters, because mailbox providers weigh how often a sender hits addresses that don't exist.
Clean the list before the next send.
A bounce report only tells you about the addresses you already mailed. The rest of the list has the same kinds of dead mailboxes in it, and each one becomes a hard bounce recorded against your domain the moment you send.
- A real SMTP mailbox check on every row, before anything is sent
- Dead and mistyped addresses split out, so they never reach your sending tool
- Catch-all, disposable and role addresses flagged alongside
Plans from $9 a month, cancel anytime, no contract. Sign in with Google and your first 100 email checks are free, no card. The free tools stay free either way.
Other 550 replies
- 550 5.1.1 — mailbox does not exist
- 550 5.7.1 — message refused by policy
- 550 5.4.1 — recipient address rejected, access denied
- 550 5.2.1 — mailbox disabled, not accepting messages
- 550 — mailbox unavailable
- 550 5.1.0 — address rejected, other address status
- 550 5.1.10 — recipient not found (Microsoft 365)
- 550 5.1.8 — bad outbound sender (Microsoft 365)
- 550 5.4.5 — daily sending limit exceeded (Gmail)
- 550 4.4.7 — message expired in the queue
- 550 5.7.26 — blocked, sender unauthenticated (Gmail)
- 550 5.7.27 — SPF authentication failed (Gmail)
- 550 5.7.28 — unusual rate of unsolicited mail (Gmail)
- 550 5.7.23 — SPF violation (Microsoft 365)
- 550 5.7.124 — sender not in allowed senders list (Microsoft 365)
- 550 5.7.509 — DMARC failed, policy reject (Microsoft 365)
- 550 5.7.606-649 — banned sending IP (Microsoft)
- 550 5.7.705 — tenant has exceeded threshold (Microsoft 365)
- 550 5.7.708 — traffic not accepted from this IP (Microsoft 365)
- 550 5.7.750 — blocked from sending from unregistered domains (Microsoft 365)
- 550 5.7.515 — authentication required for high-volume senders (Outlook.com)
- 550 5.7.1 S3140 — IP range on Outlook.com block list
- 550 5.5.0 — Mailbox unavailable (Outlook.com, Hotmail)
- 550 5.7.12 — Sender not authenticated by organization (Microsoft 365)
- 550 5.7.513 — Blocked by the recipient's own block list (Microsoft 365)
Sources
- Source: Google Workspace Admin Help: Gmail SMTP errors and codes
- Source: Microsoft Learn: Email non-delivery reports and SMTP errors in Exchange Online
- Source: RFC 3463: Enhanced Mail System Status Codes
Provider wording is quoted only where the provider publishes it.
Last reviewed 2026-10-22