Guide
Cutover, staged, hybrid or IMAP: choosing the migration route
Updated
The route decides the effort, and the effort decides the quote. Microsoft publishes the constraints, so this is one part of the scoping conversation you can check for yourself.
The routes from an on-premises Exchange Server
Microsoft documents three types of email migration from an existing Exchange Server: cutover, staged and hybrid (Microsoft Learn). Which one applies depends on your Exchange version and your mailbox count.
- Cutover migration (and Express migration)
- Everything moves at once. Microsoft's guidance applies it to Exchange 2003, 2007, 2010 and 2013 with fewer than 2,000 mailboxes, and adds that although up to 2,000 mailboxes can be moved this way, it is more reasonable to migrate 150 users or fewer because of how long creating and migrating that many users takes.
- Staged migration
- Mailboxes move in batches. Microsoft's guidance applies it to Exchange 2003 or Exchange 2007 with more than 2,000 mailboxes.
- Hybrid migration
- On-premises and online mailboxes coexist and users move gradually. Microsoft's guidance applies it to Exchange 2010 with more than 150 mailboxes and up to 2,000, to Exchange 2010 where you want small batches over time, and to Exchange 2013 or later.
The other routes
- IMAP migration
- Used for Gmail, Outlook.com and other IMAP-capable systems. Microsoft states that only the items in the user's inbox and other mail folders are migrated: contacts, calendar items and tasks cannot be migrated with IMAP, and it does not create the mailboxes, so each target mailbox must exist first. Mail sent to the source after the migration completes is not brought across.
- PST import service
- For organisations with many large PST files, Microsoft's Import Service uploads them over the network or by shipping a prepared drive. Often a distinct workstream with its own effort and its own line in a quote.
- Cross-tenant migration
- Moving mailboxes from one Microsoft 365 tenant to another, the merger and divestment case. See tenant-to-tenant migration.
- Working with a partner
- Microsoft's own guidance points to working with a partner where none of the standard routes fits the organisation. That is exactly the case where scoping quality matters more than headline price.
How the route shows up in the price
- Cutover concentrates effort into a short window, often a weekend, so more of the labour lands at out-of-hours rates. It is simple, and simple usually means cheaper overall for a small organisation.
- Staged and hybrid spread work across normal hours but run for longer and require coexistence to work correctly throughout. More elapsed time, more configuration, more consultancy.
- IMAP looks cheap and is, for the mail transfer itself. The cost lands in what it does not move: calendars, contacts, tasks and mailbox permissions have to be handled another way or accepted as a loss.
- PST and archive ingestion is often the single most underestimated line, because the data volume is discovered rather than known at quoting time.
Ask any prospective partner which route they intend to use and why, before comparing prices. Two quotes proposing different routes are quotes for different projects.