Nowadays, Office 365 suite is one of the best platforms for organizations to maintain their work continuity. Office 365 comes as a package and with so many unique features.

At the time of merging businesses, the need to migrate data from one Office 365 tenant to another tenant arises in many organizations. Apart from this, some other scenarios also may emerge the need to perform Office 365 tenant to tenant migration. 


In this article, we will walk you through step by step process to migrate the data from one Office 365 tenant to another Office 365 tenant. Let’s get started!

Office 365 Tenant to Tenant Migration

Before proceeding towards the process, users need to keep certain things in mind as mentioned below:

Important Client considerations

  • For Outlook 2010 and Outlook 2013: Delete the Microsoft Outlook account
  • In Outlook 2007 and Outlook 2010: While restarting, auto-discover will configure the client and recreate the OST file
  • For the Lync Clients: Add contacts once the merging process gets finished

Domains Licensing

  • You need to increase the licenses in Target Office 365 tenant so that all mailboxes of the source tenant can be migrated to target tenant.
  • Generate the Administrator accounts in target and source tenants, which is required in the process of migration Office 365 to another Office 365.

End-User Communications 

In order to communicate the migration to the end users in an organization:

  • Make a plan to communicate/ data migration and initiate with the notification of the data migration process between two Office 365 tenants and a few modifications with services.
  • Once the migration is done, the nickname cache has to be cleared out on the entire MS Outlook client.
  • Tell users the process to connect to Outlook Web App by using the new sign-in details if they have any problem after migration.

Step 1. Preparation

Preparation and Pre-migration Activities: Before 3 Days

Domain Preparation

Follow the steps given below to prepare the domain:

  • Start the verification of domain on target tenant for the source email domain
  • In the target Office 365 admin center, add the source domain and generate TXT records in DNS for verification

Note: The verification will fail as the domain is still in use in the other domain.

Following these step allows DNS record time to propagate. This can take up to 72 hours.

Migration Scheduling

  • Create a master list of user mailboxes that you want to move.
  • Then, generate mailbox mapping.

Mail exchanger record (MX record) time to live (TTL) test and disable directory sync in the source domain. 

Source Tenant Preparation

Before switching to the target tenant, the primary email domain should be eliminated from all objects in the source tenant

  • If the set up with SharePoint Online public website, first set the website’s URL back to the initial domain.
  • Erase all Lync licenses in the source tenant with the help of Lync admin portal.
  • Reset default email id on source mailboxes to the initial domain and reset all email addresses on all Distribution Lists, Rooms and Resources to the initial domain, in source tenant.

Target Tenant Preparation

This includes the complete verification of source domain in the target domain. Wait for one hour once you remove the domain from the old tenant.

  • If you are using AD FS, you need to configure the new domain in target for AD FS.
  • Start the activation of target tenant and assign licenses to the new user account.
  • Set the source email domain as the primary email address.
  • Set password on all mailboxes in the target domain, if you are not using AD FS or password sync feature
  • Verify testing of mail flow to or from new mailboxes in the target tenant.

Step 2. Perform Migration

In order to minimize the downtime and inconvenience, pick the best way to migrate.

  • If you want to migrate 400 or less users: Migrate Mails, Contacts, and Calendars into the target tenant mailboxes. If possible then, limit the mail migration by date. For instance, data of the last 6 months.
  • If you want to migrate more than 500 users: Utilize a multi-pass technique where you need to move contacts, calendars and 1 week of email of all the users. After that, ensure days or week and use multiple passes to fill in the mailboxes along with older email data.

After all, this, begin the migration of mailboxes using a reliable third-party tool (Microsoft also recommends using an automated solution to perform mailbox migration). Repeat the migration steps to transfer complete mailboxes to the new email domains.

Step 3. Post Cleanup

There are some essential things to keep in mind after performing the migration. This will ensure the safe and complete Office 365 migration.

  • Provide new email address and password to each employee
  • Clear the nickname cache (if any) from all the Outlook clients

The manual method should be followed very carefully and a small mistake can lead to a permanent loss of data. It is time-consuming and requires technical expertise to execute.

 


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