Office 365 Tenant-to-Tenant Migration_ What You Need to Know.pdf

Office 365 tenant-to-tenant migration aren’t just about copying files. Admins have to re-map user accounts, reassign licenses, and keep things running smoothly so staff can keep working without hitting downtime. For instance:

1. Office 365 Tenant-to-Tenant Migration:
What You Need to Know


A tenant-to-tenant migration isn’t just about relocating mailboxes to a new tenant. You’re
moving users, Teams, SharePoint sites, and files. In other words, basically everything
people touch every day. Get it wrong, and meetings vanish, chats disappear, and
permissions break. People notice fast.
Email outages, broken Teams chats, or lost permissions can grind a business to a halt.

2. These projects usually surface during mergers or divestitures. One company gets absorbed,
and suddenly, IT is tasked with stitching identities, domains, and data into a new tenant.
The catch?
Microsoft doesn’t provide a one-click way to do this. Everything from DNS cutovers to
configuring conditional access rules has to be planned out well and executed with precision.

What is a Microsoft 365 Tenant?
Microsoft 365 tenant is pretty much your company’s private slice of Microsoft’s cloud. When
you subscribe, each tenant is set up as a distinct, isolated environment linked to the
organization’s chosen domain. That slice holds your users, mailboxes, SharePoint sites,
Teams, licenses, and all security controls tied to your domain.
Tenants don’t bleed into each other. A mailbox in Tenant A doesn’t talk to Tenant B unless
you set up federation or migrate. That separation is great for security but creates friction
when data and identities need to move.

Office 365 tenant-to-tenant migration aren’t just about copying files. Admins have to re-map
user accounts, reassign licenses, and keep things running smoothly so staff can keep
working without hitting downtime. For instance:
●​A project manager still needs to access her Teams channels mid-migration.
●​Mail flow must continue without MX record failures.
●​Compliance settings, like retention labels, can’t just vanish in the process.
That’s why tenant-to-tenant projects are considered among the most intricate moves inside
the Microsoft 365 world.

3. Why Businesses Need Tenant-to-Tenant
Migrations
Companies don’t choose tenant-to-tenant migrations on a whim. They happen because the
business itself is changing, and IT has to keep up. When companies merge, split, or spin off
divisions, moving an existing Microsoft 365 tenant usually becomes unavoidable. Microsoft
points out a few ways to tackle these moves, depending on how messy the setup is.
​​Mergers and acquisitions – Two companies come together, but their users sit in
different tenants. Running both creates duplication and confusion. Consolidation
gives staff a single place to work.
​​Divestitures and spin-offs – When a unit is carved out, its mailboxes, files, and
permissions must be moved into a new tenant without breaking compliance rules.
​​Regional splits – Some firms migrate by geography, setting up a separate tenant to
meet data-residency or privacy regulations.
​​Rebranding and domain alignment – A new brand or domain often requires all
users to move under one tenant.
​​Licensing and cost control – Multiple tenants mean overlapping subscriptions and
scattered policies. One environment is cheaper and easier to secure.
Why it matters
Fragmented tenants mean higher costs, messy identity management, and frustrated users
bouncing between environments. For leadership, the cutover isn’t just an IT exercise; it’s
what makes a merger or split tangible. Until the systems are unified, the organizations
aren’t.

7 Factors to Consider in a Tenant-to-Tenant
Migration
Planning tenant-to-tenant migrations is more about preparation. The technical cutover
usually takes days, but the groundwork can stretch into months. A few factors drive how
complex the move will be:
1. Identity and Directory Management
User accounts sit at the core. Every mailbox, file, and Teams space is tied to an identity.
Admins have to choose between syncing directories, building new ones, or mapping

4. accounts by hand. Miss here, and you’ll see duplicate users, broken logins, or missing
rights.
2. Domain and DNS Dependencies
Switching domains is more than updating MX records. Mail flow Autodiscover, SPF, DKIM,
even hybrid connectors — yeah, all of it might need fiddling.
And if DNS decides to lag? Emails bounce, meetings get missed, and the bosses start
breathing down IT’s neck
3. Licensing and Subscription Alignment
Licenses purchased under the source tenant don’t automatically move. IT has to check
what’s active, what’s redundant, and whether new subscriptions are needed before
migration. Skipping this step risks leaving users without access to critical services the
moment they log in.
4. Data Volume and Workload Scope
Are you only moving mailboxes? Or does the project include OneDrive, SharePoint, Teams,
Planner, and compliance data? The more workloads involved, the more careful the
sequencing must be. For example, Teams channels reference SharePoint sites in the
background — miss that link, and collaboration breaks.
Microsoft recommends avoiding single-event migrations bigger than 15,000 users or 7 TB of
site content
, since too much at once can choke networks, slow data transfer, and
overwhelm your helpdesk.
5. Security and Compliance Controls
Security and compliance remain a crucial aspect of tenant-to-tenant migrations. Retention
labels, conditional access policies, and DLP rules don’t always transfer cleanly. Each one
has to be reviewed and rebuilt in the target tenant to avoid violations. This is where IT and
compliance officers must work hand in hand.
6. Continuity During Transition
Most migrations aren’t single-event migrations where everything switches at once. Users
need to send and receive email, schedule meetings, and share files while the move is in
progress. That requires continuity planning — calendar federation, mail routing, and
temporary syncs between tenants.

5. 7. End-User Impact
Even a perfect back-end migration fails if end users can’t work. Communication plans,
training, and support desks need to be ready. Something as small as profile photos not
carrying over to Teams can create noise if expectations aren’t set upfront.

Types of Tenant-to-Tenant Migrations
Tenant-to-tenant migrations don’t come with instructions that make sense at first glance.
Every move is a little messy. How it happens depends on what’s moving, why, and how
much the business can tolerate going offline. Usually, there are three ways IT teams handle
it:
1. Mail-Only Moves​
Just email. Nothing else. Fast. Cheap. But not foolproof. Forget an alias, misconfigure MX
records, or skip a forwarding rule, and someone misses an important client email.
2. Full Workload Moves​
This is the monster. Mailboxes, Teams, SharePoint, OneDrive, Planner—everything.
Dependencies pile up. Teams channels rely on SharePoint sites. Planner tasks sit in
channels. Miss one, and your users won’t just notice — they’ll start shouting at IT. Every file,
every permission, every link matters.
3. Phased or Hybrid Moves​
Move things in chunks. Mailboxes first, SharePoint later, Teams last. Reduces downtime but
adds juggling. Calendars have to talk to each other. Emails have to keep flowing. Temporary
syncs are tricky. One misstep and chaos erupts.
Here’s a reality check. No migration is neat. Even “small” moves can spiral. A full move
takes planning, patience, and a lot of double-checking.
And users?
They don’t care about your plan. They just want things to work.

6. Best Practices for Tenant-to-Tenant Migrations

Migrations aren’t about clicking buttons. They’re about surviving the chaos without losing
your mind — or the company’s data. Here’s what actually helps:
1. Start with a full inventory​
Know what you have. Mailboxes, Teams channels, SharePoint sites, OneDrive folders, or
Planner tasks. Don’t guess. Missing something now will certainly bite you later. Trust me,
someone always notices a lost Teams chat.
2. Map dependencies​
Teams talks to SharePoint. Planner lives in Teams. OneDrive links break if permissions
aren’t synced. Draw a map. Or scribble it on a whiteboard. Just make sure you know the
chain before you start cutting.
3. Plan for continuity​
People still need email, calendars, and files mid-move. That means temporary syncs,
calendar federation, and mail routing. Ignore this, and the chaos lands squarely on your
helpdesk.
4. Test, test, test​
Pick a small group and move them first. Check mail flow, Teams, SharePoint, OneDrive,
Planner. If it works for them, scale. If it doesn’t, tweak and repeat. Migration is an
experiment you can’t wing.
5. Communicate with users​
Send heads-up emails, guides, and alerts. Expect confusion and yes loads of questions. A
user locked out of Teams is angrier than a delayed report. Set the right expectations before
the storm hits.
6. Document everything​
Every step, every workaround, every unexpected hiccup. You’ll need it for audit trails,
compliance, or just to survive the post-migration “why isn’t my chat there?” panic.

7. 7. Have rollback plans​
Stuff breaks, mail flow halts, and permissions vanish. Be ready to reverse or patch quickly.
No one cares how neat your plan was if people can’t do their jobs.

Conclusion
Tenant-to-tenant migrations are never simple. Every mailbox, Teams channel, SharePoint
site, and file can be affected. You can miss a channel, forget a key file, and problems
appear fast. The way through needs to be methodical, where you take stock of everything
that moves. Track how each piece connects. Test with a small group first and keep the
users informed every step along the way. When it works, the transition happens quietly.
With the right steps, especially with expert support like Infrassist — the transition becomes
smooth and clean. Planning a tenant-to-tenant migration? Talk to us and we’ll help you map the right migration
path.

FAQs

1. How long does a Microsoft 365 tenant-to-tenant migration take? ​
Depends on size and scope. A few mailboxes? Days. Entire workloads with Teams,
SharePoint, OneDrive? Weeks, sometimes months. Testing and coexistence planning take
up most of the calendar.

2. Can users keep working during Microsoft 365 tenant-to-tenant migration? ​
Yes, if you plan coexistence carefully. Mail routing, calendar federation, and temporary
syncs are key. Skip them, and users hit downtime.

3. Will all data transfer cleanly? ​
Not always. Teams chats, Planner tasks, retention policies, and permissions often need
tweaking in the new tenant. Expect some manual adjustments.

8. 4. Do licenses move automatically? ​
Nope. Licenses bought in the old tenant stay there. IT needs to check who gets what in the
new tenant, buy extra if needed, and assign them before users log in.

5. What’s the biggest migration mistake? ​
Assuming it’s “just email.” Dependencies, identities, and compliance rules can bite you
hard. Small oversight, big headaches.