How we migrated 3000 users from G Suite to O365

About the Company

The company is a manufacturing firm with 20 global locations, having 3000 users in G-Suite.

Migration Objectives

As G-suite offered a very limited space to each mailbox the company wanted a solution that offers more resource capacity. The following components/features of a Gmail inbox needed to be migrated to Office 365 mail.

  • Emails
  • Contacts
  • Calendars
  • Secondary Calendars
  • Labels (primary label converted to folder; other labels discarded)
  • Tasks


  • High volume of e-mail data requires high bandwidth.
  • Migration must be done without interrupting G-suite operations until the MX record of domain is pointed to Office365 .
  • Track and prevent migration data loss.

Objectives of the Case

The users should be able to use G-Suite until the MX is switched to Office 365 and users that have been fully migrated to Office 365 should be able to start use Office 365. Once migration has been completed and MX is switched can decommission the G-suite.

How we did it?

We used Cutover method to migrate 3000 user mailboxes from G-suite to Microsoft Office 365.

Advantages: –

  1. Fastest, simplest form of migration.
  2. Users can start using all components of Office 365 immediately.
  3. New mails are received in the target messaging system.
  4. Old mails are migrated in a single pass.

The steps :

  1. Imported the users from G-suite in a CSV file format and uploaded it in Office 365 to create the users in bulk.
  2. We created a subdomain domain on G-Suite end which is used to route(forward) new e-mails from G-suite to Office 365.
  3. We then created a CSV file containing the set of users who want to migrate. CSV files containing 150 users in each file total of 20 batches were created for migration (150 is recommended limit of users in 1 migration batch by Microsoft).
  4. This file was uploaded in Exchange Admin Centre (EAC) and after providing the needed service account credentials to access G-suite started the migration batch from EAC in Office 365.
  5. After all migration batches have been completed, the users were able to use their migrated mailboxes on Office 365 as their primary mailbox.
  6. A manual MX record update for the primary domain then points to the Office 365 tenant instead of the G Suite tenant.
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