Since then, Teams has taken the lead and Groups have concentrated on a new mission of delivering a membership and access service to applications like Teams. The collaboration landscape within Office 365 changed upon the general availability of Teams in March 2017. It’s unlikely that Outlook Groups have kept pace and now has 25 million active users, but it’s possible.

The latest figure for Office 365 is 258 paid seats ( April 2020). In April 2017, Groups (now called Groups in Outlook) had 10 million active users, or roughly 10% of the Office 365 user count at the time. Given that the bulk of work that had been migrated to Office 365 at that point was email, Groups looked pretty good. Groups introduced a group mailbox to host discussions and a shared calendar and came with a SharePoint Online team site for document storage, including a shared group OneNote notebook. In the on-premises world, many Exchange organizations combined distribution lists with public folders to give people an archive for discussions. Teams didn’t exist at that point and although Microsoft’s marketing muscle was pushing Yammer (bought in June 2012) as the future for collaboration and a replacement for email (that strategy really worked out), the bulk of interpersonal electronic collaboration occurred over email.

When Microsoft introduced Office 365 Groups (now Microsoft 365 Groups) in November 2014, they were characterized as a new way for email-centric collaboration. The reason why this happens is clouded in history. Figure 1: Outlook for Windows displays some high unread counts for Groups The History of Groups

Windows 10 mail shows unread mail