When you use Outlook Client synchronization, there is a button in Microsoft Dynamics CRM for Outlook that will force the synchronization to happen. If you use server-side synchronization, this button will no longer be available to you.
For CRM On-Premises users, you will find SyncDiagnosticTool.exe in the Microsoft Dynamics CRM\Server\bin folder. Run this tool from command prompt, specifying the GUID of the organization and the GUID of the mailbox.
