When an external person is invited to a Microsoft Team, a guest account is automatically created for them. If you are the owner of a Team with any guests, you may periodically receive an email from Microsoft as part of an "access review" to confirm that guest access is still required.
Owners of a Team can then approve or deny guests for their Teams. If no action is taken, guest accounts may be automatically removed from these Teams.
The access review email will look like the following and be sent from: MSSecurity-noreply@microsoft.com
Example Microsoft Teams guess access review email (PDF 156KB)
The "Start Review" button will take you to a page where you can review guests in any Teams for which you are the owner. You can either approve or deny the guests who are listed with their access details.