January 10, 2021

Microsoft Office 365 tenant to tenant migration


In certain scenarios such as mergers and acquisitions, rebranding or divestitures, companies might have to consolidate two Microsoft 365 or Office 365 tenants for full collaboration and reduction of complexities in business operations. The process involves migration of Microsoft 365 infrastructure and services, such as Exchange Online, Microsoft Teams, OneDrive for Business and SharePoint Online from source tenant to target tenant.

In this blog, we will explore the basics of the process of Microsoft 365 migration from one organization to another. Let’s begin.

Pre-migration Planning

Step#1: Prerequisites for preparing migrants

Step#2: Domain preparation

  • Firstly, the target tenant should have sufficient space to receive all data from the source tenant which could entail obtaining additional licenses.
  • Secondly, creation of admin accounts is must for both the tenants.
  • Thirdly, the target tenant should create user mailboxes, resource mailboxes, and distribution groups.
  • Then, it is also necessary to perform Active Directory Domain Services (AD DS) consolidation using AD DS tools.
  • Lastly, train your employees on how to use Microsoft 365 post-migration.

Step#3: Domain verification

  • Firstly, initiate the process of verifying the target tenant domain in Microsoft 365.
  • Then add source domain in the admin center of the target Office 365 and create TXT records in DNS.

Step#4: Scheduling the Migration

  • Firstly, generate a list of user mailboxes for migration and create CSV file for mapping.
  • Note down the lowest value of Time To Live (TTL) on the Mail Exchanger (MX) record of the primary email domain.
  • Next, disable the directory sync for the source tenant.

Step#5: Facilitating the migration

  • Firstly, change the primary MX record to an inapproachable value to stop the flow of inbound mail to the source tenant. Here, the lowest value of TTL on the MX that you recorded will help.
  • Secondly, ensure that you removed all objects from the primary mail domain in the source tenant before migrating Microsoft Office 365 mailbox to another account.
  • Lastly, verify the source tenant in the target domain. 

The Migration Step

Step#1: The two methods for migration based on the number of users

For migration for less than 500 users, the IT admin team should use a cut-off date to limit the volume of data that is migrated. For instance, one can migrate only mail and calendar data from the last six months. For migration for more than 500 users, the IT admin team can use a multi-pass approach. The initial migration can transfer calendar, email and contact information from the last week. Then, over the next few weeks, they can transfer older data.

It is advisable to use Microsoft Solution Provider if users in your organization exceed the 500 limit or you have a huge amount of SharePoint data to migrate. Additionally, the IT admin team can use vendor-provided tools to monitor the migration progress and should send progress updates to management involved in the migration efforts. Further, while Outlook 2007 and 2010 will sync every users’ entire mailbox, Outlook 2013 can be configured with a cut-off date to limit bandwidth use.

Step#2: SharePoint Online and OneDrive migration

Aligning SharePoint and OneDrive for Business data needs careful considerations. There can be an enormous amount of data where unlike mail data, the documents keep changing frequently. In single event migrations, the required UPN changes during the migration will require re-mapping the source to the target.

Step#3: Migrating user accounts to a new domain

There are several approaches you can take to move user accounts from an existing domain to a target domain. For instance, you can use third-party tools, or hire Microsoft Consulting Services (Active Directory Migration Service) or a Microsoft partner. Be clear about which properties you want to migrate with the user accounts. For example, if you are planning to migrate the Exchange Legacy DN property, it will allow users to revert to old emails.

Post-migration stage

When the migration is complete, users must recreate their mobile profiles. Client software needs to be reconfigured (Outlook, OneDrive for Business Sync Client, Microsoft 365 apps activation). Next, it is important for users to clear their nicknames and auto-completion caches. This will prevent users from receiving NDRs continuously when replying to migrated emails.


Merger and acquisition is a common business scenario where undertaking Microsoft 365 tenant to tenant migration becomes imperative for the successful alliance of two organizations. Importantly, it helps users to use their existing accounts seamlessly even after the change in the organization’s framework.

However, this endeavor brings some unique coexistence challenges which makes it difficult for even the most competent IT teams to accomplish a merger without issues. Hence, it is recommended to seek a bit of expert advice to avoid repeated encounters with sticky problems. We, at Cyclotron, have assisted thousands of clients in simplifying their migration process making it easy and hassle-free for them.

To know more about us, please visit our website https://cyclotrongroup.com/ or reach out to us at sales@cyclotrongroup.com

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