Microsoft Exchange Online email delays: what happened and what to do

If your business uses Microsoft 365, you probably noticed something odd on 2 June: emails that should have arrived in seconds were taking an hour or more. Microsoft confirmed a widespread disruption affecting Exchange Online customers across North America, Europe, and Asia-Pacific, with some messages queuing far longer than anyone would want.

The cause was a bottleneck deep in the mail transport system. The part of Exchange Online that handles incoming and outgoing messages hit a hard limit on how many connections it could process at once, and started holding new messages in a queue while it tried to catch up. If you saw error messages, they likely read something like “The maximum number of concurrent connections per resource forest has exceeded a limit” or “Connection was closed abruptly.” In plain English: too much email hit the system at the same time, and it couldn’t keep up.

This was not a security breach. No email was lost. Messages just got stuck and eventually came through once Microsoft’s engineers scaled up the processing limits and cleared the backlog. It was disruptive, but it wasn’t a data incident.

What to check now

If your business relies on Microsoft 365 email for anything time-sensitive, two things are worth doing:

• Check the Service Health dashboard. Log into the Microsoft 365 Admin Center, go to Health > Service Health, and look up incident EX1331830. This confirms whether your account was affected and shows the current status.
• Run a mail-flow trace. Open the Exchange Admin Center and run a trace to see which messages got delayed or bounced. That gives you a record if you need to explain delays to clients or query an SLA credit with Microsoft. One thing to avoid: don’t set up manual workarounds that bypass Exchange Online’s normal routing. Microsoft has flagged that these can interfere with recovery operations and make things worse for your whole organisation.

The bigger picture

This outage followed a separate Teams and Office-on-web disruption earlier the same week. For businesses where email underpins everything, whether that’s a property management firm in Prestatyn chasing conveyancing deadlines, or an accountancy practice in Ruthin with clients waiting on year-end figures, these incidents are a reminder that cloud services are still infrastructure, and infrastructure still fails. The question is whether you find out via a client complaint or via a monitoring alert.

If your team felt this one, Dragon Digital handles Microsoft 365 monitoring for businesses across North Wales, so when something like this hits, you’re not the last to know.

For businesses already thinking about how Microsoft 365 fits into their day-to-day, our Microsoft 365 support for North Wales accountancy practices is worth a look if you’re in that sector.