Date/Time:  2026 12 Nov, 17:20 GMT:

Office 365 Email Delivery Delays 
Looks like for about the last hour, Microsoft M365 is not accepting mail.

We are seeing a lot of SMTP Responses like the following:

451 4.7.0 Temporary server error. Please try again later. PRX5 NextHop: substrate-int.office.com. RemoteHost: YT4PR01CA0040. Network Error: 10054 [BN5PEPF00046988.namprd02.prod.outlook.com 2026-11-12T19:10:01.241Z 08DF40E72E786C13]

The messages are not being lost / rejected, but deferred, and we will retry the messages periodically.

Official Microsoft Announcement:
Microsoft service health status

Also

Microsoft 365 down? Current problems and outages | US

Unfortunately, since it looks like M365 can't accept mails, there isn't any other action accept to wait.

Update:  20:00 GMT

From: Microsoft service health status
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Current status: We're aggressively pursuing all pathways to reduce impact. As a precaution, we've paused all deployments and configuration changes while we review recent changes for any correlation to this event. We've determined that the elevated load isn't driven by an overall increase in traffic, but by a large number of servers being unexpectedly unavailable, which is shifting load onto the remaining infrastructure. We're investigating what's causing these servers to become unavailable while we work to safely return them to service. 

Next update by: Thursday, November 12, 2026, at 10:00 PM UTC (about 2 hours from now)

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