Microsoft's popular Exchange service has been hit by a major downtime, locking out users for almost nine hours.

What made it worse was that it happened during day time in the US with customers being unable to send or receive emails both online and via Outlook. Customers in other countries were not affected.

The Exchange admin status page indicated that "Engineers have identified an issue in which a portion of capacity that facilitates connectivity to Exchange Online services has entered into a degraded state."

Users took to Microsoft's Office 365 community forum to vent their frustration, criticising the company not only for the downtime but more importantly for the lack of communication over the issue.

Microsoft has service health pages for Azure and status dashboards for Office 365 admins to help them monitor service availability.

At the time of writing however, the company had yet to issue a formal statement about the downtime.