Teams Add-in Disrupts Outlook Classic; Microsoft Urges Update and Repair
Microsoft says enabling the Teams Meeting Add-in can render the classic Outlook unusable for some users on older builds. The workaround is to update Outlook or run an Online Repair; Microsoft is also investigating associated email-sync errors (0x800CCC0F, 0x80070057) and notes earlier fixes to encrypted emails and a recent Exchange Online outage.