Jun 21, 2016

In The Trenches: Stress-free Exchange to Office 365 Migration

In the Trenches: Stress-free Exchange to O365 Migration
Avoid These Pitfalls
Migrating from an on-premise Exchange environment to Office 365, can be a straightforward process if you know what you are doing and where the hiddendangers are lurking.  In the past, 2-3 years that we've been delivering these migration engagements, we have built up a list of things that could disrupt or derail your migration process. 

In this post, I've collaborated with our lead migration specialists to put together a list of the most common pitfalls to avoid when migrating from Exchange to 0365.  Hopefully, seeing this list in advance of your migration, will allow you to overcome these things and better prepare yourself and your end-users.

1. Deleted Delegates

Certain migration methods only move mailboxes, mail users, mail contacts, and mail-enabled groups.  If any other AD objects, such as a user mailbox that is not migrated to O365, you must remove them from the object before the migration.

Let's take the example of delegates on mailbox accounts. Confirm with your Exchange team that these accounts are migrating at the same time as your account in order to maintain your access.

Moreover, take some time to clean up deleted delegate accounts.  The batch will give you an error.  If the owner of a group has been deleted, the group will also not migrate successfully.

2. UPN Suffix Updates

Within Active Directory, a User Principal Name (UPN) is the name of a system user in an e-mail address format.

Microsoft recommends and best-practices dictate that UPNs match users' email addresses in order to make everything simpler for the average worker.

Instead of remembering different user names and formats for logging into different resources, users can be told to just log into resources with their email address and password. Easy, right?

Even if the Active Directory forest and domain use a .local domain suffix, you can still add additional suffixes for use with User Principal Names.

So, your user's old login could be user1, but their UPN could also be [email protected] Both formats will function equivalently when accessing AD and Office 365 resources.

The problem with this is if you have a large environment and user principal names don't match email addresses for hundreds or thousands of users currently in Active Directory. Then what?

Luckily, if you have Exchange 2007, 2010, or 2013 in your environment, you can use PowerShell or a tool to quickly modify the UPNs of your users.

3. Deleting Mailboxes During a Migration

There should be no cleanup activities performed during the migration.  It is best to educate your users and request any deletions be performed before you start your batch.  If they delete a mailbox during the migration, you will have to manually delete the user from the batch and then go delete the user's mailbox in o365.  If they did this for 100s of users, you can see where that would be a huge pain.

4. Migrating Contacts and Security Groups

We have found that the IMAP migration technique does not migrate Exchange user contacts and security groups.  If you want to those to move along with the mailboxes, here is how to do it.

To achieve this, you must ensure the synchronization of Active Directory between your on-premise Exchange and O365.  In other words, how do you extend your user directory to the cloud?  The simplest way is with the Active Directory Sync Tool (DirSync).  This tool can be downloaded and installed on a Windows Server machine in your environment, and once configured it will synchronize users to the Cloud / O365 directory.

As an added benefit, you can use DirSync to sync passwords as well, and you can be granular on what OU's you plan on syncing.

5.  Failing to Disable Exchange Auto Disover Broadcast

As long as Auto Discover is setup properly, Outlook clients will experience very little disruption after the mailbox finishes moving to Office 365. Usually, it is a pop up window that says, “Your Exchange Administrator has made a change that requires you to restart Outlook.”

The user then closes Outlook and re-opens Outlook. After a minute, they may see another pop up with the same message. After closing Outlook and re-opening one more time, they should be configured properly and connected to Office 365. What is happening on the backend is fairly straight forward.  The mailbox move process flags the mailbox and changes it to a Remote Mailbox with a remote routing address of [email protected] (depending on the version of Exchange on the Hybrid server the remote mailbox may be labeled differently).  Outlook sees this change and attempts to Auto Discover the new configuration information.  When the remote routing address is found, it attempts another Auto Discover with that address and resolves the needed configuration information from Office 365.

Some phones will also use Auto Discover to resolve the needed settings after the mailbox moves.

6. Managing Permissions on Shared Resources

Within Exchange there are a number of ways people can share information, mailboxes, and calendars. When migrating to O365, this can create pain points with during migrations.

One of the most common pain points with mailbox moves to the cloud is when people access shared mailboxes.  An example might be a team accessing a shared mailbox for sales inquiries, or an Executive Assistant accessing multiple mailboxes to help manage the mail of Senior Management.  In the latter scenario, the Executive Assistant is granted Full Access permissions to the shared mailbox by the Exchange administrator, along with Send-As permissions to be able to send out emails as the shared mailbox email address. They’ll find the mailbox displayed in Outlook alongside their own mailbox.

Once this user has been migrated to O365, it is no longer possible for that user to open a mailbox on-premises such as a shared mailbox.  The shared mailbox has also has to be migrated.

Our recommendation is to group users together so shared mailboxes or resource mailboxes are moved when the users that need access to them are moved.


Hopefully, these notes will help you to have a smooth, stress-free migration and positive user experience while migrating to Office 365.  Please reach out if you think our team can help you with your migration event.

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