To control which email domains can send emails to a team channel, you must configure the email integration settings within the Microsoft Teams admin center. The org-wide settings contain an "Email integration" section where an administrator can specify a list of accepted domains. By adding contoso.com and fabrikam.com to this allowlist, you ensure that only emails originating from these domains can be successfully delivered to channel email addresses, meeting the requirement.

A. Azure AD External collaboration settings manage guest user access and B2B invitations, not the flow of email to Teams channels.
B. Accepted domains in Exchange Online define domains for which the organization handles email delivery, a much broader setting not specific to Teams channel restrictions.
D. A global teams policy manages user-facing features within Teams, such as channel creation or messaging options, not backend email integration rules.

- Microsoft. (2023). Manage email integration in Microsoft Teams. Microsoft Learn. Retrieved from https://learn.microsoft.com/en-us/microsoftteams/enable-features-office-365#email-integration. (This document outlines the org-wide settings for Teams, including the "Email integration" section where administrators can "Allow or block specific domains" for sending emails to channels.)

- Microsoft. (2023). Manage Teams settings for your organization. Microsoft Learn. Retrieved from https://learn.microsoft.com/en-us/microsoftteams/manage-teams-settings. (Under the "Email integration" section, it details the control to "Accept channel email from these SMTP domains".)