As originally communicated in MC228482 (December ’20), Microsoft is making some changes to the default setting for Guests in Microsoft Teams
Beginning on February 8th, 2021, Microsoft is turning on Guest access in Microsoft Teams by default for any customers who have not configured this setting. This will bring Teams Guest capability into alignment with the rest of the suite, where the setting is already on by default.
Timing: February 8th, 2021
Admin control: Admin center UI
Action: Review and set appropriate configuration
How this will affect your organization:
When this change is implemented if you have not already configured Guest access capability in Microsoft Teams, that capability will be enabled in your tenant. With guest access enabled, you can provide access to teams and other resources to people outside your organization while maintaining control over your corporate data.
What you need to do to prepare:
Prior to this change taking effect on February 8th 2021, if you want Guest access to remain disabled for your organization, you will need to confirm that the Guest access setting is set to “Off” instead of “Service default”. Instructions for how to configure the Teams guest access settings can be found here: Teams guest access settings
Please click Additional Information to learn more.