What Is Office 365 Migration?

Why organizations migrate to Microsoft 365

Work from anywhere

Email, files, and Teams follow people across devices and locations. Start a reply on a desktop, finish it on a phone, and pull up the same files from any laptop with no VPN required. This finally retires the file-server setup that made remote work painful.

Stronger security posture

Microsoft 365 includes Defender, MFA, Conditional Access, and DLP out of the box, with no extra appliances or separate security vendors needed. Your organization's security baseline improves the day you migrate, even before any advanced configuration.

Lower infrastructure cost

You eliminate server hardware purchases and their refresh cycles. You also free up IT time by removing monthly patch windows, storage expansions, and weekend emergency calls. The recovered time is often worth more than the licensing difference.

One place to collaborate

Outlook, Teams, SharePoint, and OneDrive share one login and one file layer, so people co-author the same document in real time and see each other's edits as they happen. No more emailing versions back and forth, or wondering which copy is current.

Scales with you

When your team grows, you just add more licenses instead of buying and setting up a new server. This makes it easy to scale up during rapid growth, acquisitions, or seasonal hiring without spending on hardware you may not need later.

Ready for what's next

Features like Microsoft Copilot require your data to already live in Microsoft 365 because they are cloud-only. Migrating now means you are ready to adopt new capabilities as they arrive, without needing a separate project later.

Common migration scenarios

Where you're migrating from matters more than where you're going. An Exchange server, a Google Workspace tenant, and a pile of PST files each need completely different tooling and prep. These are the starting points we see most often.

On-premises Exchange → Exchange Online

The classic move: mail, calendars, contacts and often public folders leave an Exchange 2013/2016/2019 server for the cloud.

Google Workspace → Microsoft 365

Gmail, Google Drive and Calendar are mapped across to Exchange Online, OneDrive and SharePoint — a cross-platform move with format differences to reconcile.

Tenant-to-tenant consolidation

Mergers, acquisitions and divestitures that combine or split Microsoft 365 tenants, carrying users, mailboxes, files and identities between them.

Hosted email or IMAP provider

Mailboxes on a hosting provider such as GoDaddy or Rackspace move to Exchange Online — often with domain ownership to transfer too.

PST import & archive cleanup

Scattered PST files and legacy archives are ingested into online mailboxes and archive mailboxes so nothing is stranded on endpoints.

Office 365 migration methods

There are several migration paths you will come across most often. Choose based on your source system and how much transition time you need. For a full side-by-side comparison of these methods, see our dedicated migration methods comparison page

Cutover Migration

How it works

All mailboxes move together in a single pass, and users reconnect afterward. It suits smaller organizations that want to move in one go.

Best for

Small organizations on a single Exchange environment
Teams that want to move in one go
Exchange 2003, 2007, 2010 sources

Watch out for

Users must reconfigure Outlook profiles afterward
The whole domain flips at once — DNS timing is critical
No coexistence period — all-or-nothing approach

Staged Migration

How it works

Mailboxes move in scheduled groups over time, while both environments stay aligned during the transition. It fits organizations that want a controlled, phased rollout.

Best for

Mid-sized Exchange 2003/2007 environments
Organizations needing controlled, phased rollout
Departments migrating at different times

Watch out for

Requires Azure AD Connect directory sync setup
Migrates user/resource mailboxes but not all object types
More complex coordination than cutover

Note: Staged migration only supports Exchange 2003 and 2007 as sources. If you're still running either of these, the migration is the easy part of your problem, since both are far past end of support and shouldn't be internet-facing. In most modern projects, the real choice is between cutover, hybrid, or a third party tool. Version limits like this are specific to Microsoft's native methods. EdbMails migrates from any Exchange version, so your source server doesn't decide your method.

IMAP Migration

How it works

Mail is copied from any IMAP-capable source into Microsoft 365 mailboxes. It is a good fit for non-Exchange sources such as Gmail, Zoho, or Zimbra.

Best for

Non-Exchange sources (Gmail, Zoho, cPanel, Zimbra)
Legacy hosted email providers
Organizations with straightforward email-only needs

Watch out for

Migrates email only — no contacts, calendars or tasks
Each cloud mailbox must be pre-created before migration
No delta sync natively — requires re-running for new items

Tenant-to-Tenant Migration

How it works

Mailboxes, files, and identities move from one Microsoft 365 tenant to another. It is common for mergers, acquisitions, and rebranding.

Best for

Company mergers and acquisitions
Corporate divestitures splitting one tenant into two
Rebranding with new tenant structures

Watch out for

Native Microsoft tooling is very limited here
Identity, domain and license mapping must be planned carefully
SharePoint/Teams permissions need manual recreation

Google Workspace Migration

How it works

Gmail, Contacts, and Calendar are mapped and moved to Exchange Online. It suits organizations switching from Google to Microsoft.

Best for

Organizations switching from G Suite to Microsoft 365
Mergers between Google-first and Microsoft-first companies
Teams consolidating onto a single platform

Watch out for

Gmail labels map to folders, so nested labels need review
Recurring meetings and shared calendars need checking after the move
Google accounts must be prepared with API access before migration starts

How to choose the right migration method

Most guides tell you to pick a method by mailbox count, but that is not the whole story. The right choice depends on your source system, how much coexistence you need, and what data you cannot afford to lose. Answer these questions before you commit, because switching methods halfway through means redoing the endpoint setup and often re-migrating data.

Quick rule of thumb: cutover suits smaller organizations, staged suits mid-sized ones, hybrid suits larger or phased rollouts, IMAP suits non-Exchange sources, and tenant-to-tenant tooling suits Microsoft 365-to-Microsoft 365 moves.

Questions worth answering before you commit

How many mailboxes, and how big?

Mailbox sizes shape the method and timeline. The overall volume of data, not just the user count, is what really affects how long the move takes.

How much coexistence do you need?

Do old and new systems need to interoperate during the move? Hybrid is the only native method that supports this fully.

What data cannot be lost?

Contacts, calendars, public folders, archives and permissions each have method-specific limits. Map them before choosing.

Are there compliance requirements?

Regulated industries may dictate tenant type, license tier, data residency and retention settings upfront.

How long does Office 365 migration take?

The honest answer is that the volume of data decides the timeline more than the number of users. A smaller organization with years of email history can take longer than a larger one with lean mailboxes. Microsoft's throttling limits also cap how fast data moves, no matter which tool you use.

In general, smaller organizations with light mailboxes can often move over a weekend. Mid-sized organizations usually run in phased batches with a pilot first, and larger enterprises plan for coexistence and migration in waves with heavier testing. Google Workspace and tenant-to-tenant moves add time for identity, calendar, and format mapping.

Pre-staging the bulk of the data ahead of time and running a short delta at cutover keeps user-visible downtime close to none, even on a move that runs over a longer period.

Migration is faster with EdbMails because the software supports multithreading and migrates up to 20 mailboxes in parallel. You can also install the software on multiple computers and migrate a different set of mailboxes on each one, running several batches at the same time for large mailbox counts.

Office 365 migration process

The method changes from project to project. The phase sequence almost never does. Failures typically cluster in two places: assessment (skipped to save a week) and pilot (cut to a single test mailbox). Both save days upfront and cost weeks after cutover.

Assess & inventory

Count mailboxes and measure their sizes
Map users, groups, permissions and dependencies
Note public folders, shared and archive mailboxes
Flag aging clients and unsupported apps

Plan & design

Select tenant type and license tiers
Choose the migration method and tool
Define batches, waves and rollback plan
Set communication and training plan

Prepare the environment

Verify domains and plan DNS changes
Provision users, licenses and identity sync
Configure mail flow and permissions
Remove stale accounts and junk data

Pilot & test

Move real users and mailboxes first
Validate mail flow and coexistence
Adjust the migration schedule
Collect feedback and refine the runbook

Migrate & cut over

Execute pre-stage passes ahead of time
Run a final delta sync at cutover
Switch DNS / MX when data is in place
Monitor logs and throughput throughout

Validate & optimize

Verify mail, files, contacts and calendars
Reconfigure Outlook and mobile profiles
Stand up support for the first weeks
Decommission legacy systems once stable

Office 365 Pre-migration checklist

These are the items teams most often wish they'd handled before migration day rather than during it.

Define the goal

Write down why you're migrating and what success looks like — it settles later trade-offs.

Inventory everything

Mailboxes, sizes, shared/archive mailboxes, public folders, files and apps.

Verify your domain

Confirm domain ownership early so users can receive mail the moment they're switched.

Right-size licenses

Match Microsoft 365 plans to what users actually need before you provision.

Clean up first

Archive or delete stale mailboxes and junk data — less to move means a faster, cheaper migration.

Check clients & devices

Update Outlook, Teams and OneDrive; retire versions that won't play nicely with the cloud.

Plan mail flow & DNS

Know exactly which records change, and when, to avoid mail sitting in limbo.

Prepare people

Tell users the what and the when, and give them training and a support channel.

Run a pilot

Migrate a test group and validate before you commit the whole organization.

Schedule wisely

Run heavy passes in low-traffic windows and leave room for a delta at cutover.

See our complete Office 365 migration checklist for the full list you can work through with your team.

Office 365 Migration Challenges and Solutions

Every migration runs into at least one of these common challenges. Here is what each one looks like and the fix that actually works. For a deeper look at each issue and its resolution, see our detailed Office 365 migration challenges guide .

Microsoft throttling slows down the migration Throttling

Microsoft applies throttling limits on data transfers to protect its cloud infrastructure. When too much data moves at once, transfers slow down or stall, and entire migration waves can get stuck waiting to resume.

Fix Break the migration into smaller batches, pre-stage the bulk of the data ahead of time, and schedule heavy passes during off-peak hours. EdbMails Office 365 migration tool handles Microsoft throttling automatically. It manages transfer rates, retries failed items, and runs concurrent mailbox migrations in parallel so the migration keeps moving without manual intervention.

Large mailboxes drag the timeline Throughput

Very large mailboxes take a long time to move. Combined with throttling, they can stall the entire migration wave and push your schedule back.

FixGet users to archive or delete old items before the move. Pre-stage the bulk in the background while people keep working, then run a short delta sync at cutover. If a mailbox keeps failing, spread it across additional passes. EdbMails supports incremental delta sync and parallel migrations to handle large mailboxes efficiently.

Public folders and permissions get overlooked Scope gaps

Public folders, shared mailboxes and permission structures are easy to forget and hard to reconstruct later once the source is decommissioned.

FixEdbMails migrates public folders and shared mailboxes while preserving the folder structure, and carries over inbox rules.

Old clients and apps break Compatibility

Outdated Office versions and unsupported add-ins are a leading cause of post-migration support tickets and user frustration.

FixUpdate or replace clients and enforce modern authentication before the move begins.

Office 365 Migration best practices

None of these are complicated, and none are optional. The migrations that go badly are almost always the ones where the team skipped the audit to save a week, then spent three weeks aftercutover rebuilding permissions and hunting for public folders that never moved.

For a complete walkthrough of each practice with real-world examples, see our Office 365 migration best practices guide.

#01

Plan more than you migrate

Thorough assessment and design prevent the surprises that turn a weekend into a fortnight.

#02

Always pilot first

A representative test batch reveals throttling, permission and client issues at low cost.

#03

Pre-stage, then delta

Copy the bulk of the data in the background while people keep working. At cutover, run one finaldelta pass to pick up whatever changed. Done right, users notice nothing except a new Outlookprofile prompt.

#04

Use modern authentication

Encrypted channels and OAuth-based auth are the baseline for a secure migration.

#05

Clean before you move

Deleting stale data cuts migration time, storage cost and complexity in one stroke.

#06

Monitor and validate

Track logs during the move and verify mail, files, contacts and calendars after it.

#07

Migrate in off-peak windows

Run heavy passes when the network is quiet to keep the business running normally.

#08

Support the first weeks

A staffed hypercare period after go-live is what turns a migration into an adoption.

Native tools vs. EdbMails

Microsoft's built-in tools handle straightforward moves, but the gaps become painful fast once a migration gets more complex: missing permission mapping, limited reporting, and no tenant-to-tenant support. EdbMails is built to cover exactly those gaps.

Included free with Microsoft 365

Native Microsoft utilities

Best suited for

Standard Exchange 2013–2019 to Exchange Online
Simple IMAP mailboxes (cPanel, GoDaddy)
Organizations with in-house PowerShell expertise

Limitations

No folder-level permission mapping after migration
Limited item-level reporting and audit logs
No date-range or folder-level filtering per mailbox
IMAP method skips contacts, calendars and tasks
No native tenant-to-tenant tooling

Recommended third-party tool

EdbMails Office 365 Migration

What it handles that native tools can't

Built-in support for tenant-to-tenant migration
Migrates everything: contacts, calendars, tasks, not just email
Incremental delta sync, run multiple passes with no duplicates
Item-level migration reports and audit logs for every batch
Public folder and archive mailbox migration without PowerShell scripting or AD prep
Folder and date-range filtering per mailbox
Concurrent mailbox pipeline for faster, parallel migrations
No PowerShell scripting required

Download Free Trial Download button

Frequently Asked Questions

Data volume decides this, not user count. A small business with lean mailboxes can finish over a weekend, while a large enterprise with a lot of data should plan in weeks and lean on pre-staging. Microsoft's throttling also caps how fast concurrent transfers run. EdbMails is a high-performance tool that migrates 2 to 5 GB per hour per mailbox and supports parallel migration of multiple mailboxes.

Yes. By copying mailboxes and files ahead of time while people keep working, then running a final delta sync at cutover to capture the last changes, you can switch users over with little or no perceived downtime. A pilot batch, careful DNS planning and post-migration validation checks protect against data loss.

A cutover migration moves every mailbox at once and suits smaller organizations. A staged migration moves mailboxes in batches over time and fits mid-sized environments. A hybrid migration keeps on-premises Exchange and Exchange Online running side by side during a coexistence period, which is best for large enterprises that need a gradual, low-impact move. For a detailed comparison of all migration methods, see our migration methods page.

Not always. Microsoft's native methods handle straightforward Exchange and IMAP moves at no extra tooling cost. But they have real limits: no tenant-to-tenant support, no permission mapping, no repeatable delta passes, and minimal reporting. For Google Workspace moves, large environments, or regulated projects, those gaps become painful fast. That's where a purpose-built tool like EdbMails covers the gap, with tenant-to-tenant, Google Workspace, PST support, delta sync, and zero-downtime moves built in.

For migration purposes, yes — Microsoft rebranded Office 365 as Microsoft 365. You'll still see "Office 365 migration" widely used because the term is familiar, but it refers to moving into the same cloud services now marketed under the Microsoft 365 name.

Once every mailbox has been moved and verified in Microsoft 365, you can start planning to retire the on-premises server. Most teams keep it running for a few weeks after cutover as a fallback while users adjust. If you used the hybrid method, the server stays active throughout coexistence and only gets decommissioned after the last mailbox moves. Before pulling the plug, make sure DNS and MX records are pointing to Microsoft 365, all licenses are in place, and no older business apps still depend on the old server.

Both can move, but they need their own planning. Shared mailboxes typically migrate alongside user mailboxes, though you should verify delegate access and send-as permissions after the move since these do not always carry over cleanly. Public folders are a different story. They require a separate migration batch and careful hierarchy mapping, particularly if your organization has years of nested folders that people still rely on. EdbMails handles both public folder and shared mailbox migrations while keeping the folder structure and permissions intact, which avoids the manual rebuilding that native tools often leave you with.

Usually, yes. After a cutover or staged migration, Outlook will need a new profile or Autodiscover has to pick up the updated settings. Most mobile devices running the Outlook app or ActiveSync will reconnect on their own once DNS propagates, but a handful will need the account removed and re-added manually. The way to keep support tickets low is simple: send users a short step-by-step guide before the switch happens, not after.

Large mailboxes are where migrations slow down. Microsoft applies throttling limits on data transfers, so a very large mailbox takes significantly longer to move than a small one. The practical fix is to clean up before you migrate. Get users to archive or delete old items they no longer need. For mailboxes that genuinely carry a lot of active data, pre-staging copies the bulk in the background while people keep working. A final delta sync at cutover picks up whatever changed since the last pass. EdbMails supports incremental delta sync and runs multiple mailbox migrations in parallel, which cuts down the overall transfer time compared to running native tools one batch at a time.

Yes. Emails, contacts, calendars and Drive files can all move from Google Workspace into Exchange Online, OneDrive and SharePoint. The tricky part is format and structure differences between the two platforms. Google labels do not map one-to-one to Outlook folders, and Google Drive sharing permissions need to be translated into SharePoint equivalents. If these are not handled properly during migration, users end up with messy folder structures and broken access. EdbMails supports Google Workspace to Office 365 migration and takes care of these mapping differences so data lands where it should without manual cleanup.

Mailbox inbox rules can be migrated along with the mailbox data, depending on the migration scenario. However, certain Exchange-specific configurations, such as custom Exchange forms, Outlook add-ins, and integrations tied to the on-premises environment, may require manual configuration after migration. For IMAP migrations, the scope is more limited, as IMAP primarily handles email data. Contacts, calendars, and tasks require separate migration methods.

Moving data is the technical half. The other half is making sure people are not confused or frustrated by the change. Send out clear communications a week or two before migration starts. Cover what is changing, when it will happen and what users need to do on their end. If you are introducing new tools like Teams or OneDrive for the first time, run short training sessions. Set up a dedicated support channel (even a shared inbox or Teams channel works) for the first couple of weeks so people have somewhere to go when things do not look right. Running a pilot batch first gives you real user feedback to fix issues before rolling out to the rest of the organization.

It depends on the method. Cutover is all or nothing. Every mailbox moves in one pass, which is why it only works well for smaller organizations. Staged and hybrid methods give you full control over which mailboxes move and when, so you can start with a pilot group, move departments in phases, or hold back mailboxes that depend on older systems. EdbMails lets you pick individual users, specific folders, or even filter by date range within each batch, giving you granular control over what gets migrated and when.

Licensing aside, the cost of an Office 365 migration typically has three parts: the migration tool, labor, and the potential cost of downtime if the migration is not planned properly. Native tools may be free but can have limitations, while third-party migration tools are often priced per mailbox. Labor costs depend on whether the migration is handled by your internal IT team or a migration partner. For a cost-effective option, EdbMails offers an affordable Office 365 migration solution with a one-time lifetime license, including free software upgrades for life and free 24/7 technical support, so there are no recurring licensing or renewal fees. This makes it especially budget-friendly for organizations planning current and future migrations.

Yes. Microsoft Teams data can be migrated between tenants, including Teams chats, channel messages, and associated data. The migration scope can vary depending on the source and target environments.

EdbMails supports the migration of Teams chats and channels, including all supported Teams data, helping organizations move their Teams content to Microsoft 365.

The required permissions depend on the migration scenario. For tenant-level migrations, Global Administrator permissions may be required. For mailbox-level migrations, Full Mailbox Access permissions can be sufficient, depending on the migration method and configuration. In short, you may need either Global Administrator permissions or Full Mailbox Access rights to perform the migration.

Incremental migration only transfers items that are new or changed since the last pass. This avoids duplicating data that already moved and keeps the target mailbox in sync with the source right up until cutover. EdbMails runs incremental (delta) passes automatically on each subsequent run.

What is Office 365 Migration?

Why organizations migrate to Microsoft 365

Work from anywhere

Stronger security posture

Lower infrastructure cost

One place to collaborate

Scales with you

Ready for what's next

Common migration scenarios

On-premises Exchange → Exchange Online

Google Workspace → Microsoft 365

Tenant-to-tenant consolidation

Hosted email or IMAP provider

PST import & archive cleanup

Office 365 migration methods

How to choose the right migration method

Questions worth answering before you commit

How long does Office 365 migration take?

Office 365 migration process

Assess & inventory

Plan & design

Prepare the environment

Pilot & test

Migrate & cut over

Validate & optimize

Office 365 Pre-migration checklist

Office 365 Migration Challenges and Solutions

Office 365 Migration best practices

Plan more than you migrate

Always pilot first

Pre-stage, then delta

Use modern authentication

Clean before you move

Monitor and validate

Migrate in off-peak windows

Support the first weeks

Native tools vs. EdbMails

Native Microsoft utilities

EdbMails Office 365 Migration

Frequently Asked Questions

Ready to start your migration?