You need to ensure that all the sales department users can authenticate successfully during Project1...

Project1: During Project1, the mailboxes of 100 users in the sales department will be moved to Microsoft 365.

Project2: After the successful completion of Project1, Microsoft Teams & Skype for Business will be enabled in Microsoft 365 for the sales department users.

After the planned migration to Microsoft 365, all users must be signed in to on-premises and cloud-based applications automatically.

Fabrikam does NOT plan to implement identity federation.

After the planned migration to Microsoft 365, all users must continue to authenticate to their mailbox and to SharePoint sites by using their UPN.

You need to enable password hash synchronization to enable the users to continue to authenticate to their mailbox and to SharePoint sites by using their UPN.

You need to enable SSO to enable all users to be signed in to on-premises and cloud-based applications automatically.