Top Ten Things to Consider to De-risk your Office 365 Migration

on December 1, 2016

Very few organizations that are deploying Office 365 are deploying a brand new communications and productivity solution. For the most part, they will be migrating an existing service or set of services to Office 365. Over the last few years, the team at Cistel has been involved in dozens of Office 365 migrations and we’ve learned a few things along the way. This post is a summary of some of the more common challenges that we’ve encountered that can be managed with a little bit of planning and knowledge.

1. Tenant name

You will need to establish an Office 365 tenant with a unique name. The tenant name will be something like If your organization’s domain name is already taken by another tenant, don’t worry about it. You will be aliasing your domain name to the tenant with DNS records. Only the Office 365 administrator needs to know the tenant name. Your users will continue to use the same email address as before.

2. Directory Services

You will need to setup an Azure AD service for users to logon to Office 365. At a minimum you will need to setup and configure a one-way directory synchronization that replicates userids (and a few other mandatory attributes). Depending on your use case you may also want to configure ADFS to allow things like self service password resets and single sign on. It’s worth considering future use cases and putting some planning into the directory services implementation.

3. Exchange: Hybrid or Staged?

Whenever possible you will want to configure a hybrid exchange environment so that mailboxes can be moved between Exchange Online and on premise with minimal disruption to users. Exchange 2010 and newer support hybrid mode. Previous versions of exchange (2007 and older) and other mail providers (such as Gmail, GroupWise, Lotus Notes, etc.) do not support hybrid deployments. If you must use a staged migration, more planning and downtime will be required.

4. Mobile Device Reconfiguration

One of the advantages of Office 365 is mobility. The promise of working from anywhere with any device is very compelling but some devices work better with Office 365 than others. Here’s a list of currently supported mobile platforms. If you are already using Exchange Active Sync (EAS), devices that support HTTP 451 devices can seamlessly find the appropriate mailbox in Office 365 without any user impact or intervention. If your devices don’t support HTTP 451, be prepared to reconfigure them unless you have a Mobile Device Management solution such as Microsoft Intune in place.

5. Mail enabled devices and applications

Don’t forget about applications (websites, ERP, etc.) and devices (fax servers, scanners, etc.) that use email. You can setup a simple SMTP relay to handle many of these situations.

6. Personal Archives (PST files)

Are public folders in or out of scope for your migration. It can be compelling to gain control of them and move them to Exchange online, however, it can be difficult to locate all of them and the migration can consume a lot of time and bandwidth. You can leave them where they are as you won’t lose anything – they will still be unmanaged to the same extent they were before moving user mailboxes to Exchange Online. Perhaps you can address them a separate project?

7. Public Folders

Don’t forget about migrating Public folders. Some organizations have legacy public folders that may go back several versions of Exchange. There may be some compatibility issues migrating public folders depending on the versions of exchange in your environment. Additionally, aliases from legacy public folders may follow internet naming conventions (may contain spaces or reserved characters) and cannot be migrated until renamed.

8. Outlook Version

In order to connect to Exchange Online most organizations will use Outlook on windows desktops. It is not mandatory to upgrade to the newest version of Microsoft Outlook to connect to Exchange online. Many organizations may prefer to perform the Office suite upgrade as a separate project. If you are not upgrading to the latest version of the Office suite for some reason, the version of Outlook that is currently deployed may not be compatible with Exchange Online or may require some updates. Here is a list of supported versions of Microsoft Outlook clients for Exchange Online.

9. Office Version

If you are deploying Office 365 ProPlus to your fleet of desktops, there are couple of options that should consider before deployment:

  1. Deployment model: Click-to-Run or MSI
  2. Architecture: x64 or x86

The decision points for these options are complex enough that they will covered as part of a separate blog post.

10. Ongoing Patching

Depending on which deployment model option you chose for your office version you may have to rethink your Office update strategy. The Click-to-Run version of Office 365 pulls updates directly from Office 365 online. It bypasses other updates methods such as Intune, WSUS or System Center Configuration Manager. If you don’t want Office 365 to manage your updates youw ill need to update the client management policy. Here’s a good post on how to update it.

As you may have noticed, most of the challenges are around migrating to Exchange Online. Since you will probably never have to go through a migration to Office 365 more than once, we strongly suggest that you seek the help of a qualified partner or the Microsoft FastTrack Center onboarding process to help you through the process. If budget is limited and you need to chose, get help with the Exchange migration and tackle the rest on your own. If you decide to go through it on your own or want to validate the quality of the service you are getting from your partner, the following two documents may be of benefit to you:

  1. Office 365 Exchange Online Planning Questionnaire – We use this to help us understand our client environment and requirements.
  2. Office 365 Exchange Online Migration Project Plan Template – We use this as a starting point for a customized project plan for each client based on information gathered from the questionnaire.



By Colin Smith

Colin Smith is the Manager of the Microsoft Solutions Practice at Cistel Technology Inc. , a Microsoft Gold Partner headquartered in Ottawa, Canada. Colin is a frequent author and presenter. He is also a dual Microsoft MVP.  He is an MVP for Enterprise Mobility (formerly System Center Configuration Manager) who has been working with the product since SMS version 1.0. He is also a MVP for Windows and Devices for IT. He has over 25 years of experience deploying Microsoft-based solutions for the private and public sector with a focus on mobile, desktop, cloud and data center management.

Colin SmithTop Ten Things to Consider to De-risk your Office 365 Migration