You may find some clients report that they receive Spam emails from MS Teams application.
This is because of the organization allow to communicate with users that are outside your organization. If the customer requests to block the domain, you may follow the below guide: -
As an IT Admin, we are allowed to block those domains from the Microsoft Teams admin center
In the left navigation, go to Org-wide settings > External access
Select the "Add a Domain" and type the domain name to choose Blocked.
Note: You can type either enter the email address or the domain to block the emails.