Microsoft’s “New Migration Experience” from G Suite to Exchange Online

Google G Suite to Office 365 Migration

The blog posted by the Exchange development group yesterday to announce new tools to migrate from G Suite should really have been titled “migrate email from G Suite” because the solution only handles mail, calendar, and contacts. Or maybe the experience is intended to migrate the bits of G Suite that people really use and ignore Docs, Drive, and the other pieces. In any case, the Exchange guys are obviously very excited that the functionality is now rolling out and should appear in Office 365 tenants over the coming weeks.

The MRS Key to Migration

The advent of better migration tools is a good thing. Microsoft has built the migration on top of a well-known and robust foundation in the Mailbox Replication Service (MRS), which has been moving mailboxes between servers since Exchange 2010. Since its initial ability to move mailboxes from one version of Exchange to another, MRS has expanded its abilities to handle more scenarios and has moved literally millions of mailboxes from on-premises organizations to Office 365 tenants. Now it can move messages, contacts, and calendar items from Gmail to Exchange Online, treating each Gmail user as a migration request and bundling those requests into migration batches that MRS processes in the background.

There’s no great magic involved in connecting to G Suite. MRS uses the IMAP4 protocol to access and read information from Gmail mailboxes. Only 2 GB can be read from a mailbox daily. As Microsoft notes, this limit is enforced by Google (at least the limit is per mailbox). In any case, MRS will process mailboxes larger than 2 GB until they are completely moved over to Exchange Online using incremental synchronization before performing the final switchover. The process will just take a little longer (well, potentially days longer).


Some limits exist. The default for the largest item is 35 MB, but this can be increased to 150 MB by adjusting the transport configuration of Exchange Online in the target tenant. Note that the size of any message can be larger than expected because of the packaging used to preserve fidelity when messages pass between different servers. The 150 MB limit might, for instance, mean that a Gmail message of 135 MB (including all attachments) can be moved, but depending on the attachments and the format of the message, the limit might be smaller. Like for any other migration, it is a good idea to ask users due to be migrated to find large messages in their Gmail account and remove any that they don’t need to be moved.

Other limits exist in terms of the data that can be migrated. Essentially, users should be prepared to recreate rules and automatic replies and to review contacts after their mailbox is moved. Migration is all about moving mailbox data and not the settings for the Gmail account or other Google-related settings.

Cultural Changes for Users

Another cultural change facing migrated users is the change from Gmail labels to folders. The impact of this might be slight for people who only ever use the Inbox and Sent Items folders, but others who have created their own system of labels to mark and process email will need some coaching to transition to folders, understand the Focused Inbox,(which some people hate), and how Exchange Online archives messages (with retention policies or the Archive option), and other features such as OWA’s clean up mailbox.

If people have used Outlook to connect to Gmail, their transition to Outlook connected to Exchange Online should be smooth. However, their client might need to be updated to make sure that they use a supported version (and if their Office 365 plan includes it, the click to run version). The same is true for people who have used Outlook Mobile to connect to Gmail as Outlook Mobile (considered by some to be the best mobile client for Gmail). On the other hand, those transitioning from the traditional Gmail browser client to OWA will need some retraining to become comfortable with their new mailbox.

More G Suite Data to Migrate

There’s more than email to migrate when an organization moves from G Suite to Office 365. Microsoft suggests that you can move files from Team Drive to SharePoint Online, but there’s also many commercial migration products that should be considered before launching into a full-scale migration.

Going to G Suite?

If you want to go the opposite way and move from Office 365 to G Suite, Google launched the beta of G Suite Migrate in March 2019. In the early days of Office 365, it was quite common to hear about companies moving from on-premises Exchange to Gmail, but that doesn’t seem so common now.

Google’s tool supports migration from Exchange (on-premises and online), SharePoint, OneDrive for Business, and file shares, but misses out big parts of Office 365 like Teams and Planner. All of which proves that migration is a complex business and that any migration project deserves substantial up-front planning before a single byte is moved.

Administrators who move from G Suite to Office 365 need help too. Our advice is to buy a copy of the Office 365 for IT Pros eBook. The book contains far too much information to digest immediately, but it will be a source of comfort as they navigate their new home in the cloud.

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