Microsoft’s Slack competitor, Microsoft Teams, was down for hours today. Users were having issues connecting to the chat service, leaving many businesses falling back to email and the ancient form of face-to-face conversations to keep communication going. Microsoft acknowledged the outage, and the company managed to restore access for all Microsoft Teams users after around four hours of issues.

Microsoft Teams has replaced Skype for Business as the main communications tool for Office 365 users, and the software giant has been continually tweaking it with updates since its original introduction back in 2017. This appears to be the first significant outage for Microsoft Teams, and it follows several connectivity problems for rival Slack during 2018.

“We can confirm that we have fully resolved connectivity issues that some users may have experienced,” says a Microsoft spokesperson in a statement to The Verge. No reason has been provided for the outage.

Update, February 18th 1:20PM ET: Microsoft has now resolved its Teams outage.