Microsoft has started to restore email flow to Exchange Online customers affected by an outage that has lasted more than six hours.
In updates posted at around 3:15 p.m. U.S. Eastern Time to an official support forum, Microsoft representatives wrote that the cause of the problem has been identified, it's being addressed and that mail is being rerouted away from the affected systems.
The discussion thread in the Office 365 support forum is now at 14 pages, filled with comments from exasperated IT administrators and end users whose work has been affected by the outage.
Office 365 is Microsoft's cloud communication and collaboration suite for businesses, schools, government agencies and nonprofit organizations, and Exchange Online is one of its components. Exchange Online is also sold as a standalone service.
The problem apparently began at around 9 a.m. Shortly after 4 p.m., Microsoft reiterated that it was working on solving the issue via its Office 365 Twitter account, where many affected users have also complained.
It's not clear how many customers have been affected, but judging by the reaction on Twitter and the Office 365 support forum, the scope of the outage isn't trivial.
Office 365 comes in a variety of versions for businesses, schools, nonprofit organizations and government agencies that vary in price and in the applications and tools they include.
Most Office 365 editions come with Exchange Online, SharePoint Online, Lync Online and OneDrive for Business, and some also include the full-featured Office productivity app suite.
The basic version of Office 365 for Education, called A2, is free, while the most sophisticated version for businesses, Office 365 Enterprise E4, costs US$22 per user, per month and includes a 99.9 percent uptime guarantee.
Juan Carlos Perez covers enterprise communication/collaboration suites, operating systems, browsers and general technology breaking news for The IDG News Service. Follow Juan on Twitter at @JuanCPerezIDG.