Permanent failure — do not retry
SMTP 550 4.4.7
message expired in the queue
4.4.7 means your message sat in the sending queue until it expired, so the sender gave up. RFC 3463 defines X.4.7 as "delivery time expired". Exchange Online reports it as "Message expired". Every attempt was deferred, so the final NDR combines a 4.x.x code with a failure.
How it appears
550 4.4.7 QUEUE.Expired; message expired
4.4.7 Message delayed
What causes it
- The recipient's server kept deferring the message, for example through greylisting or rate limiting, until the queue timed out.
- The recipient's server was unreachable for the whole retry period.
- The recipient domain's MX records point at a server that does not answer.
- Microsoft also lists protocol timeouts and too many recipients on one message as causes.
How to fix it
In order — try the first one first.
- Check the recipient address and the domain's mail server before sending again. Resending to a server that never answers will expire the same way.
- Look up the recipient domain's MX records and check that the server answers on port 25.
- If many messages to one domain expire, the recipient's mail server is the problem. Contact them another way.
- Reduce the number of recipients per message.
Common questions
- What does SMTP 550 4.4.7 mean?
- 4.4.7 means your message sat in the sending queue until it expired, so the sender gave up. RFC 3463 defines X.4.7 as "delivery time expired". Exchange Online reports it as "Message expired". Every attempt was deferred, so the final NDR combines a 4.x.x code with a failure.
- Should I retry a 550 4.4.7 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 4.4.7?
- Check the recipient address and the domain's mail server before sending again. Resending to a server that never answers will expire the same 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 5.7.25 — no PTR record for sending IP (Gmail)
- 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
Last reviewed 2026-09-11