This document outlines the migration of 5000 users from GroupWise to Office 365 for the Amerpoort and Reinaerde organizations. It discusses using the Migration Toolkit (MTK) to migrate user mail, folders, and other data from GroupWise to Exchange Online. It also describes implementing the GWAVA Retain archiving software to archive GroupWise data before migration. The migration plan involves archiving GroupWise with Retain, migrating GroupWise archives to Retain, and migrating a limited amount of recent mail data (6 weeks) for each user while enabling client access to Office 365. Multiple test migrations will be conducted before the final production migration to move all 5000 users to Office 365.