Migrating a company to Microsoft 365 doesn’t fall apart for lack of licences: it falls apart because someone switches off the old email too soon and on Monday morning half the workforce can’t send a single message. The technology is the easy part. The hard part is doing it without anyone noticing the change, and that’s where the clean migrations part ways from the ones that end in a week of firefighting.
This guide gets straight to the point: what really changes, how you prepare the ground, how you move the email without cutting it off, the mistakes that cost you dearly, and what needs doing the day after. If you want to do it with a safety net, at the end we tell you how we handle it without stopping your business.
What you gain (and what changes) by moving to Microsoft 365
Microsoft 365 isn’t “the same old Office but in the cloud”. It’s no longer having to maintain your own mail server, having your mailbox accessible from any device, and unifying email, files, video calls and security under a single identity. For an SME that means less infrastructure to look after and fewer things that can break at six o’clock on a Friday.
What you gain, specifically:
- Professional email with your own domain, with no physical server to maintain or update.
- Files in SharePoint and OneDrive: goodbye to the shared NAS folder only one person understands.
- Teams for meetings and teamwork, using the same login as your email.
- Security built in: MFA, access policies and Microsoft’s cloud backup.
What changes for the user? Less than they fear. Outlook is still Outlook. What changes is underneath: where the mailbox lives, how it’s accessed and who answers when something goes wrong. And the bill changes: you move from an investment in servers to a predictable per-user fee that scales up and down as your team grows or shrinks.
Preparation: domain, licences and a backup first
90% of a migration’s success is decided before a single message is moved. This phase is boring and it’s the one nobody wants to pay for; it’s also the one that prevents disaster. Three pillars.
1. The domain and its DNS
Your domain is what sends email to one place or another. Before migrating you have to verify the domain in Microsoft 365 and be clear about the DNS records: MX (where the email arrives), SPF, DKIM and DMARC (which say who is allowed to send on your behalf). Changing the MX record is what redirects email to the new mailbox, and that’s why you touch it at the end, not at the start. Change it too soon and you start receiving into an empty mailbox.
2. The right licences
Not every licence does everything. Business Basic gives you email and Teams on the web but no desktop Office; Business Standard does; Business Premium adds the security layer (Intune, Defender) that many companies need and don’t even know exists. Buying wrong here means overpaying every month for years, or falling short and having to upgrade in a hurry. You size it by user profile, not by buying the same thing for everyone.
3. The backup first (this is not optional)
Before moving anything, you back up the email, contacts and calendars from the source. It seems obvious and it’s the first thing anyone in a hurry skips. A migration goes well 95% of the time; the backup is your insurance for the remaining 5%. Without a backup, a sync error means lost email with no way back.
The migration step by step without cutting off the email
The key to not stopping the business is simple to state and hard to execute: the new mailbox is filled before email is redirected to it. Never the other way round. That way, on switchover day the user already has all their history waiting for them. The order that works:
- Preparation: domain verified, users and licences created in 365, backup done.
- Initial sync: all the email from the old system is copied to the new mailbox in the background, without touching the live email. The user carries on working as normal.
- Delta sync: just before the cutover, only the new emails from those last few hours are copied. That way the new mailbox is up to date to the minute.
- MX change: the MX record is pointed to Microsoft 365. From here on, new email arrives in 365. You pick a low-traffic window (Friday evening or the weekend).
- Reconfiguring clients: Outlook and mobiles point to the new mailbox. With the sync done properly, the user opens Outlook on Monday and it’s all there.
While the DNS propagates (which can take hours) some email may still reach the old mailbox. That’s why the source mailbox isn’t switched off the same day: it’s kept alive for a few days catching the stragglers. Email is never lost because there’s always a mailbox listening.
Common mistakes that cost you dearly
Almost every migration that ends badly fails for the same reasons. None of them is a complex technical problem; they’re all about method.
- Changing the MX before syncing. The classic: you redirect email to an empty mailbox and the user panics because “everything’s gone”.
- Switching off the old server too soon. You lose the emails that were still arriving there during DNS propagation.
- Forgetting SPF, DKIM and DMARC. You migrate and suddenly your outbound email lands in spam at your clients’ end. Silent reputational damage.
- Not accounting for printers, scanners and applications that send email. The multifunction device that “scans to email” stops working because nobody reconfigured its SMTP sending.
- Not warning the team. With no heads-up beforehand and nobody to ask, every question turns into a ticket and lost hours.
- Migrating without a backup. Working without a net. When something fails, there’s no way back.
A migration is judged by what the user doesn’t notice. If nobody writes to you on Monday asking where their email is, it went well.
After migrating: security (MFA) and training the team
Moving the email is half the job. The other half begins once everything’s in 365, and it’s the half that separates “we have Microsoft 365” from “we’re protected with Microsoft 365”.
First, MFA (two-step verification) for everyone, no exceptions. A cloud mailbox with only a password is a mailbox that sooner or later ends up compromised: phishing exists precisely because it works. With MFA on, stealing the password is no longer enough to get in. It’s the security measure with the best effort-to-protection ratio there is, and in 365 it’s switched on by policy. From there it’s worth reviewing access by device, blocking automatic external forwarding and setting a sensible password policy.
Second, minimal training for the team. Not a three-day course: four practical things. Where the shared files are now (SharePoint instead of the network folder), how the second factor works on the phone, how to recover a deleted email and who to call when something isn’t working. A technically perfect migration that leaves the team lost ends up generating more tickets than an average one done with proper support.
How MagicBoxDesk does it with no downtime
At MagicBoxDesk we migrate companies to Microsoft 365 across Spain with one non-negotiable principle: the business doesn’t stop. We prepare the ground (domain, DNS, licences sized to each profile, a full backup first), we sync the mailboxes in the background while your team keeps working, and we leave the MX change for the lowest-impact window. On Monday, everyone opens Outlook and finds their email, contacts and calendar intact. No outages, no lost email, no surprises.
And we don’t leave you on your own the day after: we switch on MFA and the security policies, reconfigure printers and applications that send email, train the team and stay on as your outsourced IT department for whatever comes next. It’s part of our infrastructure and cloud services, designed so technology stops being your problem and you can get on with your business.
Thinking about making the jump to Microsoft 365, or dragging along a half-finished migration that left problems behind? We’ll review it and tell you what you really need, no smoke and mirrors. Request a no-obligation quote and we’ll plan your migration without stopping the business.
