- Cutover Migration: A cutover migration is a solution that migrates all mailboxes at once over a few days (depending on mailbox sizes), and allows you to manage email accounts in Microsoft Office 365. This is the most simplistic and least cumbersome migration solution Microsoft offers. This migration can be utilized if you are running Exchange 2003 or higher, and if there are fewer than 2000 mailboxes in your environment. However, even though the maximum number of mailboxes is 2000, it is not recommended to migrate such a high amount of mailboxes in one go. The primary domain name must be accepted by Office 365 and owned by you. Once the migration completes, each user with an on premises Exchange mailbox will be a new user in Office 365, and as a result will require their own license in order to start receiving and sending mail.
- Staged Migration: This type of migration is only possible with Exchange 2003 or Exchange 2007, and there must be more than 2000 mailboxes in your environment. As the name suggests, a staged migration migrates the mailboxes in batches that are preselected by you or the administrator of your organization. A staged migration differs significantly from a cutover migration in the sense that there are more preliminary steps that must be taken before the migrations can occur. Accounts must be synchronized between the on premise Active Directory domain and Office 365 by using Azure Active Directory sync for staged migration. Without this synchronization, a staged migration cannot be performed. Only user mailboxes and resource mailboxes are migrated, and distribution groups, contacts and mail-enabled users are migrated to Office 365 through directory synchronization (DirSync).
- Hybrid: A hybrid deployment is used if you want to migrate mailboxes in small batches over a period of time. This option migrates using an integrated Exchange Server and Office 365 environment. Both on premises and online mailboxes for your organization and is used to gradually migrate users and email to Office 365. What this basically means is both your on premise Exchange as well as Exchange Online is used simultaneously until all mailboxes are eventually migrated over a period of time. This option is only available to Exchange 2010 and 2013 with more than 2000 mailboxes.
With the right IT Support in 2016 this migration can be seamless, and the amount of downtime should be as minimal as possible. No matter what solution you choose to go with, it is always a good idea to clean up your Exchange environment. Minimizing the amount of time it takes to migrate is directly related to reducing the number of errors and problems you encounter throughout the migration process. It is recommended to reduce mailbox sizes as much as possible, i.e. multiple mailboxes with 20-30GB of data should be reduced to a more reasonable mailbox size such as 2-10GB. Getting rid of inactive mailboxes and consolidating as much data as possible will also be beneficial. Not only is migrating to the cloud beneficial in itself, but it also gives administrators an excuse (not that they should need one) to really clean up the email environment, and make sure only data that is pertinent remains. There are many angles to think about when it comes to migrating to Office 365, but that is not something a business who does not specialize in IT should have to worry about. Focusing on the core aspects of your business should always be a priority, and certainly not whether or not you should be running a Cutover Migration over a Staged Migration. Leaving those decisions to IT professionals is certainly the way to go.
Written by:
Chadd Jones
System Architects Inc. 
