HI @Amanda SerieFor the mailboxes that are using Exchange Online (O365)1. Under your email server profiles, there will be one created that will be your Exchange Online server. One important field you need to watch here is the Process Email From; Make sure you set to a date you want before you enable a mailbox to use Server Side sync2. You will need to Approve the Email addresses for each mailbox. You either need Global Admin as @Abdul Majid pointed out, or you can also do this with a D365 Service Administrator role in Office 365 as well.3. For each Mailbox then, make sure its configured with the right sync options, Outlook or Server Side sync, which sounds like it will be in your future. Also, important here is to make sure you identify the Server Profile the mailbox needs to use.For Exchange 2013 folks;1. You will have to create a new Email Server profile for Exchange 2013. You'll have to make sure the exchange web services are enabled for the Exchange server for this to work. https://docs.microsoft.com/en-us/dynamics365/customer-engagement/admin/supported-email-service-configurations-server-side-synchronization2. After this, you will have to Approve the email address for each user and Test and Enable the mailboxes like above.That should get the emails flowing again. Assuming if you are using the Outlook Client with the Outlook Sync option, the users Outlook has to be open for the whole sync and send the process to work.