421 4.4.7: Message Expired in Queue
The 4.4.7 bounce means your email spent too long in the queue without delivery and expired. Learn what causes queue expiry and how to investigate.
Published · Last verified · Maintained by TamingDNS
421
4.4.7
Message Expired in Queue
Very Common
🔢 Enhanced Status Code Breakdown: 4.4.7
| Component | Value | Meaning |
|---|---|---|
| Class | 4 | Temporary failure (Soft bounce) |
| Subject | 4 | Network and routing |
| Detail | 7 | Message Expired in Queue |
Per RFC 3463 Enhanced Mail System Status Codes. Class (X) = severity, Subject (Y) = category, Detail (Z) = specific condition.
💬 What This Error Means
Your email spent too much time in the 'waiting room.' Your server kept trying to deliver the message for several days, but the recipient's server never answered the door. Eventually, your server gave up and sent you this bounce.
Common Causes
- The recipient's mail server was completely unreachable for several days straight
- There was a long-term DNS problem that prevented your server from finding the right address
- A major network outage occurred between your server and theirs
How to Fix This
- Check if the recipient's website or other services are currently working
- Try sending the email again now. The problem that caused the delay may have been fixed
- If you're sending to a colleague, you might want to ask them (or their IT team) if they had a recent server outage
📚 Official Documentation
Microsoft 365 uses 4.4.7 when your message cannot be delivered within 24 hours. NDR typically arrives with subject "Delivery delayed".
📖 Microsoft 365 / Outlook documentation → Browse all Microsoft 365 / Outlook error codes →📋 Real-World Example Messages
These are real bounce message formats you might receive. Paste yours into the Bounce Decoder for instant analysis.
421 4.4.7 Message expired after maximum queue time 421 4.4.7 QUEUE.Expired; Message expired at
🔗 Related Error Codes
Got a bounce message to decode?
Paste your full NDR email, SMTP error line, or mail log fragment to get an instant plain-English diagnosis.
Open the Bounce Decoder →