Introducing the new migration experience from Google G Suite
Published Apr 16 2019 03:40 PM 35.3K Views

Update: Our migration from Google Workspace now uses REST API instead of IMAP. Please see this post for the announcement and go here for new documentation of the process.

Several weeks ago we added a new Microsoft 365 Roadmap item announcing our intent to add ability to migrate Google G Suite calendars and contacts to the ability to migrate mail to Office 365 using our native migration tools.  We're excited to say that this functionality has started rolling out!  You can expect to see the new features light up for your tenant in the coming weeks. Since this is a new flavor of migration to Office 365, let's take a look at what is now becoming available and answer some frequently asked questions about it.  Before diving into any migration project, it is important to answer some basic questions about it:

  1. What is the size of the organization you are trying to migrate?
  2. Based on your business requirements, would you like to migrate using a "cutover" (everyone at once) or "staged" (longer-term coexistence) approach?
  3. What is the (approximate) average mailbox size that you'd be migrating?
  4. What kind of data do you need to migrate - like mail, calendar and contacts?
  5. Given the answers to the above questions, does this migration tool fit my needs?

Answering these questions will give you some idea of the scope of your project. Then you just need to find out how to get started. And you can read all about that here. Before you actually start clicking though, let's cover some of the terms you'll need to understand and an overview of how the new G Suite migration flow will work:

Intro to Mailbox Replication Service (MRS)

Microsoft Exchange Mailbox Replication Service (MRS) is a component that handles mailbox import, export, migration and restoration for Exchange and Office 365.  Migrations are managed using individual requests.  MRS is the principal mechanism used to move mailbox data from one place to another.  In context of moving data from G Suite to Office 365 MRS is used to move mailbox data, including messages, contacts, and calendar items.  Each mailbox being migrated from G Suite to Office 365 has its own request that will be processed by MRS.

What is a migration batch?

For better usability and scheduling at scale, another component called the Migration Service provides the ability to submit migration requests for batches of users. Behind the scenes, the Migration Service uses the Mailbox Replication Service to manage the per-mailbox requests.  Grouping a set of users into a batch is primarily for management purposes and does not impact the speed or throughput of your migrations based on batch size.  For your migration, you could choose to have one batch of all users or split the users into multiple batches - the choice is yours.

Give me an overview; how do migration batches work?


How is mail data migrated?

Mail data is currently migrated using IMAP protocol.  Authentication happens using domain-wide delegated access using a Service Account that is under your control.

How fast can I migrate my data?

For mail data there is a throughput limitation of 2 GB per mailbox per day. This limit is enforced by G Suite. For contacts and calendar data, this completely depends on the quota restrictions for your tenant's service account on the Google G Suite side (because a different protocol is used to migrate calendars and contacts; please see documentation).

I reached my 2GB limit for the day (for mail) - will the migration continue the day after?

Yes - it will automatically continue once there is capacity to migrate more data, until the 2GB/day quota is reached.

What data will NOT be migrated over?

  • Mail: Vacation Settings or Automatic reply settings as well as Filters or Rules
  • Meeting Rooms: Room bookings
  • Calendar: Shared calendars, cloud attachments, Google Hangout links and event colors
  • Contacts: A maximum of three email addresses per contact are migrated over
  • Contacts: Gmail tags, contact URLs and custom tags are not migrated over

Will this also support migrating data from Google Vault to Office 365?


What is the smallest batch size and is there an optimal batch size?

A migration batch can have a single user, with no current upper limit.  There is no magic number for the best migration speed or efficiency.  We recommend creating batches per-department or another logical grouping for your organization.

What is the size of the largest email I can migrate from G Suite to Office 365?

The limitation is based on the transport configuration for your organization.  The default limit is 35MB. Please see this article on how this limit can be increased.

I tried migrating and saw mention of bad items; what are those?

Bad items are data conversion failures that may be encountered during the syncing phase.  Should you encounter any bad items, you can see these in the migration report on the user and batch levels.

How do I track progress of migrations?

You can view the progress and reports via the Exchange Admin Center or use the Get-MigrationBatch PowerShell cmdlet.

Mail on Office 365 doesn't support labels.  How is mail translated to folders?

In order to provide the best mail experience in Outlook as well as account for the Focused/Other view, we translate most labels to folders.  Mail with the 'Starred' label will become flagged.  Mail with the 'Important' label will influence its Focused/Other designation.  Mail with other labels will be copied into a folder with the corresponding label name, and mail with no other labels will be moved to the Archive folder.  This means that some items that had multiple flags in G Suite will appear in multiple folders in Office 365.

I started off a batch in EAC, why doesn't my migration make progress?

Please make sure that you went through all of the pre-requisite steps on the G Suite side and have provisioned users on the O365 side.  Also check the per-user error messages if you see users with a status of 'Failed'.

My messages have completed copying but my migration is stuck at 95%. Help!

This could be expected.  Check the status of migration batch; if it reached the 'Synced' status, you can choose to complete the migration batch.

What does completion do?

For G Suite migrations, there's an option to complete a batch.  During completion, an additional incremental sync of data is performed, followed by a "switchover".  During switchover, a forwarding address is applied to the source G Suite mailbox to forward emails to the configured Target Delivery Domain.  Also, any forwarding address applied to the target O365 user is removed.

Do I really need to "Complete" my batch?

Depends - If you're taking the cutover migration route, you don't need to complete your batch(es). If you're taking the staged migration route (i.e., migrating a subset of users sequentially over a longer period of time), you'd want to complete certain batches if you'd like the automatic mail forwarding rules to reverse (Forward email from Gmail to Exchange Online instead of Exchange Online to Gmail).

How can I tell if this feature is available in my tenant?

As an Admin, you will see the G Suite (Gmail) migration option under the Migration tab in the Exchange Admin Center (EAC) or will have access to the -Gmail parameter for New-MigrationBatch CMDlet. If the feature is not available yet, please give it a few days and try again. It is still rolling out to all tenants.

What is the big deal? Why is this way of migrating better?

We believe that our customers will see multiple benefits from this new way of migration:

  • Being a first party migration experience that’s built in, there are no additional costs or set up required and no ‘per head’ migration cost (like some 3rd party migration solutions might require).
  • Ability to migrate mail, calendar and contacts with high fidelity.
  • Data is copied straight from the source to Office 365 with no rest points along the way. Be at peace knowing that your tenant’s data is migrated in isolation.
  • Service account authentication delegation: no need to have knowledge of or reset user’s credentials to migrate their data.
  • Tenant service account isolation: the service account used to migrate data is owned and controlled by you, and can only be used to migrate data into your own tenant.
  • Ability to migrate users in batches; staged migration support.
  • Settings simplification: automated mail forwarding between source and target environments for users being migrated in batches.
  • Built-in mechanism to optimize storage for Labels to Folders conversion by reducing item duplication.

We really hope you enjoy using this new set of tools and it makes your migration from G Suite to Office 365 even easier. We really want to hear your feedback, so please do leave us a comment, and feel free to ask any questions here too. We have plans to make this migration toolset even better over time, so keep an eye on the blog. The Exchange Migration Team

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