#FAQFriday: 10 Tips for Office 365 Tenant to Tenant Migrations

During the past few years, Tenant to Tenant Microsoft Office 365 / Azure migrations have become increasingly high in demand, as companies merge and acquire others.

Planning Tips:

1. Do a full discovery of the data in both the source and target tenants including users, UPNs, email addresses, resource mailboxes, shared mailboxes, groups, domains, license subscriptions, enabled applications in packages, Exchange Online protection settings/hygiene, hub rules, SharePoint data structure, OneDrive configuration, Teams settings, Power BI groups and reports, MDM preferences, Intune configuration (if available), Azure and security settings.

2. Pull reports for both source and target for the accounts, and determine if there are any duplicate names or aliases (hint: we often see duplicate names around shared mailboxes like Finance, and popular last names like Smith, Hernandez, and Patel – you can use an Excel comparison list or PowerShell to determine duplicates names across environments).

3. Review security settings, admin roles, permissions, and password policies to determine if there are differences between the source and target tenant. If there are, talk with the business groups or your customer to determine how the source accounts will change when they are migrated to the target tenant.

4. Create a test strategy that includes:
  • Test a migration with a few test accounts in a lab setting or without impacting live users.
  • Test with a few patient IT pilot users. Allow “bake time”.
  • Test with a larger group of IT pilot users. Allow “bake time”.
  • Test with a few patient non-IT pilot users. Allow “bake time” before migrating more accounts.
  • Run statistics with your test accounts and pilot users to determine how fast the data and mailboxes can be copied from the source to target accounts.

5. Determine the types of accounts and objects that will be included in a directory sync / password sync / Azure ADConnect (users, shared mailboxes, resource mailboxes, security groups, distribution groups, contacts).

6. Any accounts or objects that are not included in a sync can be recreated manually or imported into the target Office 365 tenant with a CSV import and PowerShell.

7. Once the new accounts are created in the target tenant, (unless they are hidden,) they will most likely begin to accumulate mail from the users who are already in the tenant.
To avoid this problem, you can either create a connector from the target Exchange Online to the source Exchange Online, or add  mail forwards to route mail from the target mailboxes to the source mailboxes.

8. If there is a lot of data to migrate, plan to seed a copy of the older mail data first into the target accounts, for example, older than 60 days.
  • If you decide to seed a copy of mail data, plan to only include the messages (don’t include calendar meetings, contacts, tasks, and rules).

9. Plan for an entire weekend (or a couple full business days) for the domain cutover, replication, and last passes of data if you are working with a complicated environment.

10. Keep in mind that a domain can only be in one tenant at a time, and a domain cannot be moved from a source domain to a target domain unless all references to it have been removed from the source domain. This includes UPNs, email addresses, Exchange Online rules, public folders, Office 365 group aliases, Skype for Business addresses, Teams addresses, and Power BI objects.

We hope you found this blog useful! It's been created based on our years of experience engineering dozens of tenant-to-tenant Office 365 migration projects, including some that involved long nights of troubleshooting to prevent outages.