Estimate how long your email migration to Microsoft 365 will take based on mailbox count, data volume, connection speed, and migration complexity.
| Source Platform | 1–25 Mailboxes | 25–100 Mailboxes | 100–500 Mailboxes |
|---|---|---|---|
| On-Premise Exchange | 1–2 weeks | 2–4 weeks | 4–8 weeks |
| Hosted Exchange | 1 week | 1–3 weeks | 3–6 weeks |
| Google Workspace | 1–2 weeks | 2–5 weeks | 5–10 weeks |
| IMAP Provider | 1–3 weeks | 3–6 weeks | 6–12 weeks |
| POP3 Provider | 2–4 weeks | 4–8 weeks | 8–16 weeks |
Timelines include planning, testing, migration, and post-migration support phases. Actual timelines vary based on data volume, internet speed, and complexity. View full Cloud Email details
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A straightforward migration for under 50 mailboxes typically takes 1 to 2 weeks including planning, testing, and cutover, while larger organisations with hundreds of mailboxes or complex legacy systems can take 4 to 8 weeks. Total data volume and connection speed both have a significant effect on the timeline.
The biggest factors are total mailbox data volume, upload bandwidth available for the migration, the source email platform's compatibility, and how much testing and staff training is built in before go-live. Migrations from legacy or heavily customised on-premise Exchange servers generally take longer than moving from another cloud platform.
With proper planning, most migrations are designed to avoid extended downtime - mail continues flowing throughout, with a brief cutover window, often outside business hours, when accounts switch over. A staged migration approach, moving batches of users at a time, further reduces the risk of disruption to daily operations.
Migration speed depends heavily on available bandwidth and the source platform, but many providers can move roughly 5 to 20GB per mailbox per day under typical conditions. This estimator factors in mailbox count, total data volume, and connection speed to give a realistic project timeline rather than a generic average.
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