Migrate from On-Premise Exchange to Microsoft 365

Running an Exchange server in your own walls — security updates, backups, certificates, ageing hardware — is expensive in time and risk. Moving to Microsoft 365 hands all of that to Microsoft while keeping Outlook and the same addresses. The good news: depending on the size of your organisation, there's a method suited to transferring mailboxes, calendars and contacts without downtime, and it can be run cleanly, step by step.

What gets migrated — and the three possible methods

From a local Exchange server you transfer complete mailboxes (emails, folders, contacts and calendars stored server-side), shared mailboxes and distribution lists. Microsoft offers three official approaches depending on the size of the estate:

• Cutover migration: ideal up to a few dozen mailboxes. Everyone switches at once, with no long coexistence.
• Staged migration: for larger estates on older Exchange versions, in successive batches.
• Hybrid migration: for large organisations that want lasting coexistence between local Exchange and Exchange Online, with a shared address book and a gradual cutover.

Step 1 · Audit the Exchange environment

First, take inventory:

• Exchange version (2013, 2016, 2019…) and patch level — it determines the available methods;
• number and size of mailboxes, shared mailboxes and meeting rooms;
• the state of Active Directory and whether to sync via Microsoft Entra Connect;
• DNS/MX records, Autodiscover and certificates; lower the TTL to 300 seconds before cutover.

This audit settles the central question: cutover, staged or hybrid. Below a few dozen mailboxes, cutover is often the simplest.

Step 2 · Provision Microsoft 365

Set up the tenant, add and verify the domain, assign licenses. For a sizeable estate, deploy Microsoft Entra Connect to synchronise Active Directory accounts to the cloud: users keep the same sign-in, and the directory stays consistent. Don't change the MX records yet.

Step 3 · Migrate the mailboxes

The migration is driven from the Exchange admin center (Migration > Migrate to Exchange Online). For a cutover migration, the tool connects to your server via Outlook Anywhere (RPC over HTTP) and copies all mailboxes — mail, contacts and calendars included — into Exchange Online. For a hybrid migration, the Hybrid Configuration Wizard (HCW) links the two organisations and lets you move mailboxes on demand while keeping seamless coexistence.

In every case, the copy runs in the background while the local server keeps receiving mail. A final delta pass catches the last messages before finalising each mailbox.

Step 4 · Files and shared drives

Exchange does not handle files, but a cloud migration is the right moment to tidy your data: move network drives and working folders into OneDrive (personal data) and SharePoint (team data) using the OneDrive client and the SharePoint Migration Tool. Verify permissions once the transfer is done.

Coexistence is your safety net: as long as the local server and Exchange Online run in parallel, no email drops, and you can switch users at your own pace.

Step 5 · Switch DNS/MX and Autodiscover

Once the mailboxes are copied, point the MX records to Microsoft 365 and update the Autodiscover record (CNAME to autodiscover.outlook.com) so Outlook finds the new mailboxes automatically. Add Microsoft's SPF, enable DKIM and publish a DMARC policy. Thanks to the lowered TTL, propagation takes only a few dozen minutes.

Step 6 · Verify and reconfigure clients

Test delivery, then reconfigure Outlook: after the Autodiscover cutover, the profile usually reconnects to Exchange Online on its own. On mobile, update or recreate the Exchange account. Check shared calendars, meeting rooms and delegations, then decommission the local server only once coexistence is finished.

Common pitfalls

• Rate limits: the service caps migration throughput per mailbox; a large mailbox can take several hours.
• Duplicates: re-running a full migration instead of a delta duplicates messages.
• Recurring calendars and delegations: complex series and delegate permissions should be checked first after cutover.
• Autodiscover: a forgotten record stops Outlook from finding mailboxes — the number-one cause of post-migration tickets.
• Premature decommissioning: never turn off the local Exchange server before validating every mailbox and internal mail flow.

How much it costs: Yuna7 vs an IT contractor

Having a contractor migrate on-premise Exchange to Microsoft 365 often costs several hundred dollars, with quotes and lead times. Yuna7 automates the cutover and you only pay for what you actually use — you can even try it for free.

Let Yuna7 migrate on-premise Exchange to Microsoft 365 for you

Describe your migration in one sentence: Yuna7 audits your Exchange server and picks the right method (cutover, staged or hybrid), provisions Microsoft 365, launches the mailbox copy, tidies your files into OneDrive and SharePoint, switches DNS/MX and Autodiscover at the right moment and verifies everything arrived — you simply approve the sensitive steps. Far cheaper than a technician, and launched in minutes.