Why businesses move to Microsoft 365
Most businesses that move to Microsoft 365 are coming from one of a few situations: a basic hosted email provider that is starting to feel limited, an on-premise Exchange server that is ageing and expensive to maintain, or a free email setup (sometimes still running on the domain registrar bundled email) that is not professional enough anymore.
The reasons for moving are usually practical:
- Better spam and phishing filtering. Microsoft invests heavily in email security and the filtering in 365 is significantly better than most basic hosting providers.
- Access to Teams, SharePoint, and OneDrive as part of the same subscription.
- Larger mailboxes (50GB or 100GB compared to the 1-5GB you get with cheap hosting).
- Better mobile experience with the Outlook app.
- Easier administration for your IT provider.
- Microsoft handles the server infrastructure, patching, and uptime.
It is not a magic solution to every problem, but for most businesses, the combination of email, file storage, video conferencing, and collaboration tools in one subscription is hard to beat.
What the migration actually involves
An email migration is not just a case of flicking a switch. Here is what happens in a typical migration for a business with about 20 people.
Planning (1-2 weeks before). Your IT provider sets up the Microsoft 365 tenant, adds your domain, creates user accounts, and configures the basic settings. They will also audit your current email setup to understand mailbox sizes, distribution lists, shared mailboxes, aliases, and any email rules or forwarding that need to be recreated.
Data migration. Your existing emails, contacts, and calendar entries need to be moved to the new mailboxes. For most migrations, this is done using a migration tool that copies data from the old server to Microsoft 365 in the background while everyone continues using their old email. Depending on how much data there is, this can take anywhere from a few hours to a couple of days.
DNS cutover. This is the critical moment. Your MX records (the DNS settings that tell the internet where to deliver your email) get changed to point at Microsoft 365 instead of your old provider. Once this happens, new email starts flowing to the new system.
Post-migration cleanup. Reconfiguring Outlook on every workstation, setting up the Outlook app on phones, testing that email is flowing correctly in both directions, and sorting out any issues that crop up.
Common problems and how to avoid them
DNS propagation delays. When you change your MX records, it can take up to 48 hours for the change to propagate across the internet. During this window, some emails will go to the old system and some to the new one. A good migration plan accounts for this by keeping the old system running and monitored until propagation is complete.
Missing emails during cutover. If the old email system is shut down before DNS has fully propagated, emails can bounce. This is the most common cause of lost emails during a migration. The solution is simple: keep the old system running for at least 72 hours after changing MX records.
Large mailboxes taking too long. If someone has a 30GB mailbox full of attachments, migrating it takes time. Start the data migration well before the DNS cutover so the bulk of the data is already across.
Outlook profiles. After migration, Outlook on each workstation needs to be reconfigured to connect to the new Microsoft 365 mailbox. On modern versions of Outlook with autodiscover properly configured, this is usually automatic. On older setups, it might need doing manually.
Shared mailboxes and distribution lists. These are easy to forget in the planning stage. Make sure every shared mailbox, alias, and distribution list is documented and recreated in Microsoft 365 before the cutover.
Email signatures. If your old system had centrally managed email signatures, you will need to set these up again. Microsoft 365 has basic signature capabilities built in, or you can use a third-party tool for more control.
Realistic timeline for a 20-person business
Here is what a well-planned migration looks like:
- Week 1: Planning, audit of existing setup, Microsoft 365 tenant setup, user account creation.
- Week 2: Start background data migration (copying existing emails to new mailboxes while old system continues running). Configure shared mailboxes, distribution lists, and any mail flow rules.
- Week 3: DNS cutover (ideally on a Friday evening to give the weekend for propagation). Reconfigure Outlook on all workstations. Set up Outlook on mobile devices. Test everything.
- Week 4: Monitor for any issues, decommission old email system once you are confident everything is working.
So roughly three to four weeks from start to finish. Simpler setups can be quicker. More complex environments with multiple domains, lots of shared mailboxes, or large amounts of data will take longer.
What your team needs to know
Before the migration: Let everyone know what is happening and when. Tell them their password will change and they might need to log in again on their devices. Ask them to clean up their mailbox if it is enormous (delete old emails with large attachments they no longer need).
During the migration: There might be a period where email is slightly slower than usual as DNS propagates. If they notice anything odd (missing emails, delivery failures), they should report it immediately rather than waiting.
After the migration: They will need to log into Outlook with their new Microsoft 365 credentials. Their mobile email might need reconfiguring. They should check that their email signature is correct and that their calendar entries have come across properly.
The most important thing is communication. People get nervous when you mess with their email, and rightly so. Keep them informed at every stage and have someone available to help with any issues in the first few days after cutover.
One more thing
Take the opportunity to set up MFA (multi-factor authentication) on all Microsoft 365 accounts during the migration. You are already disrupting everyone is routine by changing their email, so adding MFA at the same time means only one period of adjustment rather than two. And it is genuinely the most important security measure you can put in place.