Web and mobile clients are reporting issues. Outlook client may also experience issues and email may not successfully send.
It seems Microsoft is re-licensing which temporarily removes the current license.
Close out of Outlook for roughly ten minutes and then re-open Outlook. If any emails were bounced back or did not send during this time, they should be resent.
9/20/2021 11:11am
Any emails that were bounced back or did not send to or from Groups or dl- mailing lists should be resent.
9/17/2021 1:03pm
9/17/2021 10:02am
Depending when your license is affected, you may need to close out of and re-open Outlook.
9/17/2021 9:21am
9/17/2021 9:13am