4.4.7: message expired in the queue

What it means

Exchange Online returns this after it has tried to deliver a message for 24 hours without success. Each attempt met a temporary refusal, a timeout or no answer at all, so the service kept the message queued until it expired, then sent this report. Microsoft writes it as 550 4.4.7: the 4.x.x code records that the underlying failures were temporary, while the report itself is final and the message will not be retried. Most often the destination is at fault: its server is down, its MX record is wrong, or it refuses Microsoft servers. Sometimes the cause sits on the sending side, in SPF, an expired domain or a hybrid connector, or in a directory conflict reported as AmbiguousRecipientTransientException.

Common causes

• The destination mail server is offline, unreachable or refusing connections from Exchange Online.
• The destination domain has a missing or wrong MX record.
• A network problem made every delivery attempt time out.
• Two directory objects share the recipient address, so Exchange Online cannot resolve the recipient (AmbiguousRecipientTransientException).
• A hybrid connector to the on-premises organization no longer matches its IP addresses or firewall rules.

How to fix it

1. 01Check whether only one destination domain is affected; if so, tell the recipient by another channel and pass on the remote server name and error from the report.
2. 02The destination's admin should check the domain's MX and DNS records, for example with the Outbound SMTP Email test in Microsoft Remote Connectivity Analyzer.
3. 03If other domains are affected too, test your own tenant with the same analyzer and check that your SPF record lists every source of your mail.
4. 04Confirm with your registrar that your domain has not expired.
5. 05In a hybrid setup, give the report to the on-premises admins, who may need to rerun the Hybrid Configuration Wizard.

Sources

What this page rests on, checked on 20 Oct 2026. The explanation is ours; the reply text is the server's.

• Fix NDR error "550 4.4.7" in Exchange Onlinelearn.microsoft.com
• Email nondelivery reports and SMTP errors in Exchange Onlinelearn.microsoft.com

Further reading

• MX lookup
• SPF lookup