Allow External access in Microsoft Teams

Let your Teams users chat and communicate with users in another Teams organization

• You have users in different domains in your business. For example, Rob@ContosoEast.com and Ann@ContosoWest.com.
• You want the people in your organization to use Teams to contact people in specific businesses outside of your organization.
• You want anyone else in the world who uses Teams to be able to find and contact you, using your email address. If you and another user both enable External Access and allow each other's domains, this will work. If it doesn't work, the other user should make sure his or her configuration isn't blocking your domain

This method will guide us on how to allow external users to Microsoft Teams

1. Login to https://www.office365.com/
2. Sign in using Global Administrator account 
3. Navigate to Microsoft Teams admin center  
4. In the left navigation, go to Org-wide settings > External access
5. At the top of the External access page, click External access to On
6. If you want to allow all Teams organizations to communicate with users in your organization, skip to step 7.
7. If you want to limit which organizations can communicate with users in your organization you can either allow all but some domains or only allow specific organizations. To allow all but some domains, add the domains you want to block by clicking Add domain. In the Add, a domain pane, put in the domain name, click Blocked and then Done. To limit communications to specific organizations, add those domains to the list with a status of Allowed. Once you have added any domain to the Allow list, communications to other organizations will be limited to only those organizations whose domains are in the Allow list.
8. Click Save
9. Then make sure the admin in the other Teams organization does these same steps. For example, in their allowed domains list, their admin needs to enter the domain for your business if they limit which organizations can communicate with their users.