Migrating to Microsoft 365 seems simple on the surface — sign up for licenses, move the data, point the DNS records, and you're done. Right?
Not quite. After 12+ years of performing migrations from Exchange, Google Workspace, hosted providers, and between M365 tenants, we've seen the same mistakes trip up organizations over and over. The technology part of a migration is actually the most predictable piece. It's the planning, communication, and edge cases that catch people off guard.
Here are the seven most common mistakes we see — and how to avoid them.
Mistake 1: Underestimating the Data Volume
Companies often don't realize how much data they actually have. A 200-person organization with 10 years of email history can easily have multiple terabytes of mailbox data. Add in shared mailboxes, public folders, personal archives, and file shares, and the total data volume can be staggering.
Without proper scoping, migrations take longer than expected and can blow past maintenance windows. We've seen organizations quote themselves a weekend migration that actually needed three weeks of background syncing to complete properly.
The fix is straightforward: audit your environment before you commit to a timeline. Count your mailboxes, measure your data volume, and identify your largest mailboxes and shared resources. This gives you a realistic scope — and a realistic timeline.
Mistake 2: Skipping the Pilot Migration
Testing with a small group first reveals configuration issues, permission problems, and unexpected data formats before they affect the whole organization. Skipping this step is the single most common cause of migration emergencies.
A pilot group of 5-10 users — ideally a mix of regular users, heavy email users, and people with complex mailbox setups — gives you a controlled environment to validate the entire process. You can confirm that email flows correctly, calendars sync properly, contacts are intact, and any shared resources work as expected.
If something goes wrong with 5 users, it's a fixable problem. If something goes wrong with 500, it's an organizational crisis.
Mistake 3: Forgetting About Shared Resources
Mailboxes are just the start. Public folders, shared mailboxes, distribution lists, room and resource calendars, and shared drives all need to be part of the migration plan. We've seen projects stall because these were discovered mid-migration.
Public folders are especially tricky. Many organizations have years of accumulated data in Exchange public folders — some of it critical, some of it forgotten. All of it needs to be inventoried, and decisions need to be made about what gets migrated, what gets archived, and what gets retired.
The discovery phase should capture every shared resource in your environment. If it exists in your current platform, it needs a plan for the new one.
Mistake 4: Poor User Communication
Users need to know what's happening, when it's happening, and what to expect. A simple communication plan — advance notice, day-of instructions, and post-migration support contacts — dramatically reduces support tickets and frustration.
We recommend at least three communication touchpoints:
- One to two weeks before migration: what's changing, when it's happening, and what users need to do (if anything)
- Day-of migration: confirmation that the migration is happening, expected timeline, and who to contact for issues
- Post-migration: confirmation that the migration is complete, any changes to workflows, and support resources for the first 1-2 weeks
The goal is simple: no one should be surprised. When users are surprised by IT changes, they lose trust — and trust is hard to rebuild.
Mistake 5: Using Manual Methods for Large Migrations
PST exports and imports, manual forwarding rules, and one-mailbox-at-a-time approaches don't scale. Enterprise-grade migration tools pre-stage data in the background, automate the process, and ensure nothing gets lost.
If your migration plan involves USB drives and overtime, there's a better way. Modern migration platforms can sync data incrementally over days or weeks, so the final cutover takes minutes instead of hours. They handle permissions mapping, folder structure preservation, and data integrity verification automatically.
The tools matter. Using the right migration platform is the difference between a smooth weekend cutover and a week of firefighting.
Mistake 6: Not Planning DNS and Mail Routing Carefully
The actual cutover — switching MX records, updating SPF/DKIM/DMARC, and reconfiguring mail flow — is where things can go wrong fast if not planned properly. This step needs to be documented, tested, and executed precisely.
DNS changes propagate at different speeds depending on TTL settings and DNS providers. If you don't lower your TTL values in advance, you could have mail routing to the old platform for hours or even days after cutover. SPF and DKIM misconfigurations can cause your outbound email to land in spam folders. DMARC failures can result in email being rejected entirely.
We build a detailed DNS cutover checklist for every migration — and we verify every record after the switch. This isn't the step to rush.
Mistake 7: No Post-Migration Validation
Migration isn't done when the data lands. Every mailbox needs to be verified — email counts, folder structures, calendar data, and contacts should all be spot-checked. Without validation, issues can go unnoticed for weeks.
We run automated validation reports after every migration to compare source and destination mailbox item counts. We spot-check folder structures and permissions. And we stay engaged for 1-2 weeks post-migration to resolve any user-reported issues quickly.
The worst thing that can happen after a migration isn't a big, visible failure — it's a small, silent one. A missing folder. A broken calendar. A shared mailbox that lost its permissions. These small issues erode confidence and create lasting frustration if they're not caught early.
The Bottom Line
Microsoft 365 migrations are not inherently difficult — but they are inherently complex. The difference between a smooth migration and a painful one almost always comes down to planning, communication, and process.
Alpachi has been performing Microsoft 365 migrations since 2012 — from Exchange, Google Workspace, hosted platforms, and between M365 tenants. We've migrated thousands of mailboxes and we've seen every edge case. If you're planning a migration and want to do it right the first time, we'd be happy to talk through your project.