- Client
- Multinational technology services group
- Sector
- Technology Services
- Services
- Microsoft 365 Migration, Cutover Management
- Year
- 2025
- Timeline
- Cutover in one weekend
- Read time
- 4 min read
600+
Users migrated with mail and OneDrive intact
30+ TB
Mailbox and OneDrive content moved
0.1%
Item error rate on validated batches
01 · The challenge
What we walked into
After its acquisition, the client needed every user's mailbox and OneDrive content moved into the acquiring group's Microsoft 365 tenant, with a single weekend set aside for the cutover. People carried on working in the old tenant right up to that weekend, so the migration had to keep pace with a live business.
The client wanted staff to arrive on the Monday with everything they relied on day to day already in place, which meant the plan had to be built on throughput we had measured ourselves rather than on estimates.
02 · Our approach
How we got there
- 01
Plan on measured throughput
We built the plan around transfer rates measured from real data, giving the client a forecast it could rely on and letting sequencing be agreed with stakeholders well in advance.
Forecasting
- 02
Track what landed
Per-user counts exported through the migration platform's API fed a live tracking workbook, so shortfalls surfaced long before cutover weekend. OneDrive transfers were monitored continuously, and stalled jobs were restarted the day they were found.
Continuous
- 03
Pilot, then scale
A pilot group proved the settings before we scaled up, and executive mailboxes were handled individually so each could be verified on its own.
De-risking
- 04
Cutover weekend
Cutover followed a runbook setting out every step by day and owner. Final delta passes ran with mailbox rules included, then excluded once mail flow switched, so nothing could overwrite changes users made in their new mailboxes.
One weekend
03 · The outcome
What changed
Staff arrived on Monday with the content they depended on already in place, older mailbox history arriving in the background on an agreed timetable. The whole cutover fit inside the single weekend it was given.
On schedule
The cutover completed on schedule, and staff started the following week with recent mail, OneDrive content, calendars, and contacts in place.
Validated against reality
Every completed batch was validated against what had landed, item by item, with 100% of in-scope items processed and a 0.1% error rate confined to known categories such as oversized items.
Ahead of the platform
When Microsoft began retiring Exchange Web Services during the migration window, the tenant configuration was verified and a fallback agreed in advance, so the migration carried on without interruption.
Technologies
- Microsoft 365
- Exchange Online
- OneDrive
- Quest On Demand Migration
A note on confidentiality
Much of our work takes place in regulated and security-sensitive sectors, where the details of a client's environment are confidential by default. In line with our commitments to those clients, identifying details in this case study have been anonymised or generalised, while the work, the decisions, and the outcomes are described as delivered.
If you would like to know more about this engagement, we are happy to discuss it further and can share additional information on request.