Without a doubt, building an Exchange hybrid environment to migrate your Exchange mailboxes to Office 365 is a significant undertaking, which is all the more difficult when small tasks need doing as they stop you moving to the next step.  There are a number of pre-planning tasks you can complete prior to starting an Office 365 migration that will make the hybrid environment build smoother and reduce the pressure on your deployment team.  So before you jump in to configuring Exchange Server and all the other major steps required to allow you to migrate, consider the following smaller tasks.