Explanation
References:
https://www.petri.com/azure-active-directory-external-collaboration-policy
Topic 1, Contoso, Ltd Case Study
Overview
Existing Environment
Contoso, Ltd. is a pharmaceutical company that has 750 users. Contoso has departmental teams spread across office in North American.
The company has a main office in Seattle and four branch offices in New York, New Jersey, Boston, and Florida.
Active Directory Environment
The network contains an on premises Active Directory domain. All users are created in the domain and are organized in organizational units (OUs). All the users use their domain credentials to sign to their computer.
Microsoft Office 365 Environment
Contoso has a Microsoft Office 365 subscription and uses the following servces:

Current Business Model
Contoso has the following business model
* The HR department has a branded site collection.
* Currently, the default storage limit is set for all the site collections.
* The marketing department uses multiple site collections created by an administrator named Admin 1.
*Contoso has a strategic partnership with a company name Litware. Inc. Litware has an Office 365 subscription. All users at Litware have a user account in the litwareirnc.com domain.
Problem Statement
Contoso identifies the following issues:
* Non-site owners invite external users to access the content in SharePoint Online.
* Users upload audio, video, and executable program files to OneDrive for Business.
* The company manages two separate identities for each user, which creates more administrative work.
* Users in the HR department report performance issues affecting their site collection. You suspect that the issues are due to large images on the home page.
Technical Requirements
Contoso has the following technical requirements for the Office 365 environment:
* Add a Yammer feed to new communication sites.
* Prevent non-site owners from inviting external users.
* Troubleshoot the performance issues of the HR department site collection.
* Increase a 100-GB storage limit for the site collection of the marketing department.
* Prevent users from syncing media files, such as MP3 and MP4 files, from OneDrive.
* Restrict users from sharing content from the finance department site collection to the Litware users.
* Ensure that SharePoint administrators do not have administrative permissions to the site collections.
* Ensure that the managers in the marketing department can view the storage metrics of the marketing department sites.
* Maintain all user identities in on-premises Active Directory. Sync passwords to Microsoft Azure Active Directory (Azure AD).
* Ensure that when users are deleted from Microsoft 365 their associated OneDrive content is retained for
90 days. After 90 days, the content must be deleted permanently.