Exchange Online migration - Expanding your Exchange to the Cloud

Cloud is mainstream – and many organizations are taking advantage of the benefits of the evergreen service provided by Office 365 to get on board with the latest version of Exchange. In this article, Steve Goodman walks through the options available. Steve is an Exchange MVP, regular blogger, conference speaker and host of the UC Architects podcast. He works as Head of Unified Communications for leading Office 365 partner, Content and Code.


For many organizations implementing the latest version of Exchange Server may be tempting, but for many mid-size businesses it can be very costly to provide high availability and large mailboxes. Exchange Online, one of the integrated components of Office 365 provides your users with always up-to-date Exchange, with 50GB mailboxes and the reliability of hosting mailboxes across multiple datacenters. To stay relevant, IT professionals with a focus on Exchange and Unified Communications need to understand Exchange Online and the wider Office 365 and Azure stack.

What’s the fuss about Office 365?

Office 365 is now a mature product; with over four years on the market and hosting some of the world’s largest businesses, it has provided a reliable product and as a suite of business productivity tools provided great value. Exchange Online has a history dating further back than Office 365 and emerged as Exchange Labs and then Live@EDU and was made available to Universities and other education customers before maturing into a core offering within Office 365.

Different organizations have a different reason to look at Office 365 as an answer, but in general the costs compare very favorably to implementing and maintaining Exchange yourself, and the set of products are pre-integrated and always evolving. Services like SharePoint and OneDrive work seamless with Exchange Online and new features like Delve, which helps you connect with relevant data, are only offered through Office 365 due to the computation power they require.

Options for Exchange Online

If you are planning on expanding your Exchange to the cloud, you’ve got a number of options. You can use Hybrid to extend your organization and migrate seamlessly, or use the migration tools available.

Hybrid Migrations

Exchange Hybrid allows you to connect your on-premises Exchange server to Office 365. In essence this provides rich co-existence between your mailboxes running on your Exchange servers and those running in Office 365. You can share email domains, send and receive secured email between cloud and on-premises, view colleague’s calendars, see free/busy and more.

Often Hybrid is most suitable for organizations that plan for a long period of co-existence and they are really expanding to the cloud rather than moving. A Hybrid implementation is most suited to those that have rich email integration with on-premises systems and cannot replace them with cloud-compatible solutions quickly or perhaps have contractual requirements for mailbox data location for some users and it will take time to resolve.

Hybrid is also great for organizations who want to see a very smooth migration process with excellent control over migration timings, the ability to move mailboxes both to and from the cloud, and minimal user inconvenience. Mailboxes moved using Hybrid use Remote Moves, based on the same technology that is used when moving mailboxes between internal Exchange servers or even between databases. This keeps key information within the mailbox and sends the correct signals to allow Outlook to automatically re-configure whilst keeping pre-cached OST data. Often all users see with a Hybrid migration is a single prompt for the password when they first re-connect to their mailbox after the mailbox migration.

Implementation of Hybrid does have some key pre-requisites. Exchange 2010 Service Pack 3, or Exchange Server 2013 with the latest Cumulative Update is a requirement. If you are running an older version then a single Exchange 2010 or 2013 server can be added to fulfil the Hybrid role and provide the “bridge” to the cloud.

In addition, Azure Active Directory Sync needs to be in place. Azure AD Sync copies objects from your local Active Directory into Office 365, and provides the right information required to allow users to login, provide a shared Global Address List and essential attributes required to make Hybrid mailbox moves work.

Staged Migrations

A staged migration is similar in some respects to a Hybrid migration as both allow you to move mailboxes across in staged batches. Staged migrations don’t move the mailbox to the cloud but instead copy the mailbox contents across in a one-shot approach, leaving the old mailbox behind for manual clean-up.

The staged migration approach uses Outlook Anywhere as the transport mechanism to move mailboxes and as such as compatible with older Exchange versions. You’ll often find staged migrations are very suitable for small organizations that want to move the cloud relatively quickly without the hassle of setting up a temporary Hybrid server, but with the benefits of a shared global address list and the ability to use Azure AD Sync to allow login with existing credentials.

Cutover Migrations

A cutover migration is in theory available for organizations with up to 2000 mailboxes but rarely used at that scale. A cutover migration connects to the on-premises Exchange organization using Outlook Anywhere and, given a list of all mailboxes, performs regular synchronization jobs copying mailbox data.

When the organization is ready to move and all data has been copied, a cutover migration mandates that all users are switched across to the new service at once.

Just like a staged migration, the seamless Outlook experience available with Hybrid can’t be used, so cutover migrations are labour intensive and require floor-walkers to visit users and reconfigure their devices, often all on the same day. Because Azure AD Sync cannot be used in combination with a cutover migration, users will require new passwords.

A Hybrid Migration can provide the same “cutover” functionality as it also provides pre-staging and regular syncing – however it is more work to setup.

Finding out more

There’s more to Exchange Online migrations and you can find out more either on or via MVP community blogs. Microsoft’s own Office 365 deployment and success sites are a great starting point to learn about the technology, find out what help you can get as in some cases Microsoft can even help you set up and migrate. Community sites give you some of the real-world experience and detailed guides on setup and usage of functionality as and when it is released. You’ll find a wealth of information on my blog