How to Fix Pending Email Error 450 4.4.316 in Microsoft 365 Exchange
Question details
The user needs to resolve an issue where email messages are stuck in a pending state with error code 450 4.4.316 and socket error 10061 after migrating to the cloud.
- Product
- Microsoft Exchange
- Device & OS
- not provided
- Scenario
- Monitoring message traces and troubleshooting mail flow interruptions following a cloud migration.
- Observed behavior
- Previous messages remain stuck in a pending state in the Microsoft 365 message trace with a connection refused error, despite new emails being delivered normally.
Ensure you have Exchange Administrator privileges in the Microsoft 365 admin portal and access to your organization's network firewall configurations.
Review Exchange Connectors and Mail Flow Configuration
Verify your organization's environment configuration and ensure that Exchange Online connectors are correctly routing mail to the intended destination.
Pending messages in the mail queue cannot be released in the same way as quarantined messages. The system will automatically retry delivery once the underlying routing or connection issue is resolved.
Error 450 4.4.316 usually indicates a transient connection issue where the target server is rejecting the connection. This is common if connectors are still pointing to old on-premises servers after a cloud migration.
Confirm whether your organization is using a hybrid environment or a fully cloud-based configuration post-migration.
Log in to the Microsoft 365 Admin Center, navigate to 'Admin centers', and select 'Exchange'.
Go to 'Mail flow' > 'Connectors'. Review the Outbound connectors to ensure they are pointing to active, correct IP addresses or fully qualified domain names (FQDNs) for your current setup.
Check Firewall Rules and Network Connectivity
Investigate network firewalls and source server settings to ensure they are not blocking incoming connections from Exchange Online.
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Frequently Asked Questions
Can I manually release pending messages in the Exchange mail queue?
No, pending messages in the mail queue cannot be released manually in the same way as quarantined messages. They are held due to connectivity issues and will be automatically retried by the server once the connection error (such as 450 4.4.316) is resolved.
What does socket error 10061 indicate in Microsoft Exchange?
Socket error 10061 means 'Connection Refused'. This indicates that the target server actively rejected the connection attempt, which is most often caused by network firewall restrictions or the receiving SMTP service being down.
Why are new emails delivered normally while old emails remain pending?
After a cloud migration, DNS records and active routes may be updated for new incoming mail. However, older messages that were generated before or during the migration might be attempting to use outdated, cached connector routes that point to servers no longer accepting connections.
