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There are certainly a lot of moving parts to consider when you plan a migration to Office 365. It's even more complicated when you have to execute the move for two different companies looking to make the cloud leap.
The decision to use Office 365 multiple tenants versus a single tenant must factor in the long-term objectives of the organizations. A configuration that uses a separate tenant for each company might seem to be the path of the least resistance for deployment and configuration tasks; however, the single tenant scenario has some drawbacks when it comes to the level of collaboration and interactions between two or more companies.
Moving to Microsoft's hosted email service Exchange Online or the full Office 365 suite can be tricky for larger organizations that have grown through mergers and acquisitions due to having multiple identities within their environments as the result of having two or more Active Directory domains. Microsoft provides some flexibility to choose between a consolidation of all companies under one tenant or a move into multiple tenants with a trust in between.
Navigating the challenges when organizations unite
Mergers and acquisitions have become more commonplace in today's business environment, which puts more pressure on IT to help deliver a smooth transition to a common IT platform. Where there were once two distinct entities, IT must facilitate communication and collaboration across company boundaries.
The method to integrate two organizations under one single identity management can be as simple as merging the two or more domains into one Active Directory forest. However, that can bring its own set of technical challenges and requires a significant amount of effort and Active Directory expertise, and most likely will involve the use of third-party tools to help with the consolidation and merger. As a result, some IT administrators will consider a simpler alternative: Keep the organizations independent and set up a trust across the domains. This approach allows them to move forward with a migration to Office 365, which would include the migration of emails.
There are certainly pros and cons to a migration to Office 365 for sister companies under one tenant or separate tenants with federation established between them. Here are just a few of the considerations.
What is the possibility of a split?
If there's a chance the companies might separate at some point, then the two companies should move to Office 365 as separate tenants. When the organizations split, each takes back their data without significant headaches. A merger of multiple companies into a single tenant will require a significant amount of effort to separate the data and migrate it out to gain access. Administrators should factor in the long-term view and gain some understanding from the business leaders to ensure they align with an Office 365 setup that will require less work during a separation process.
Do they use similar or unified IT policies for data protection and security?
When two companies unite, someone needs to run the IT department. The decision can depend on the respective IT maturity of each company, the number of employees, and the level of skill set. After this selection process, it might make sense to standardize and adopt one set of IT policies and procedures. If that's the case, then this consolidation will centralize the management of policies, compliances and licenses. The choice to use a single tenant for Office 365 will be the route to go here.
Will there be the need for a single email address domain?
There are certainly some occasions where two sister companies need to unify the email address domain and brand identity into a single entity. In that case, the only feasible option when there is an Exchange Online migration in the works is a single tenant option. This arrangement gives the companies a common email domain and allows them to continue to receive emails on the legacy domain names.
Are there any compliance requirement considerations?
There are other areas related to Exchange Online that can make a compelling case for choosing a single tenant, such as when Exchange administrators need to perform e-Discovery searches across multiple email domains. With companies unified under a single tenant, those types of compliance activities can run without the need to log on several times.
Will limits in Exchange functionality stifle teamwork?
The use of multiple tenants with federation between two sister companies does pose some limitations that can be painful for the end users and limit the level of collaboration and interactions between them. Some of these limitations include lack of visibility of calendar details between users from different companies, and lack of delegate access for calendar and emails. If any of these features are a must-have for the business users, then IT will need to look at a single tenant which would remove those restrictions.
What about other collaboration features?
The single versus multi-tenant decision affects other services beyond Exchange Online, such as Microsoft Teams and other Office 365 services. Some of the limitations that come with two or more tenants are the lack of global searches when using SharePoint.
There is also a lack of support for Office 365 Groups across multiple tenants. Users from one tenant only see users in their Active Directory forest and can only invite employees from the sister company as guests, which limits their ability to see OneDrive, shared calendars and other valuable collaboration capabilities that would be available under a single tenant setup.