Order of operations in an M365 tenant-to-tenant migration is not a formality. Get it...

Order of operations in an M365 tenant-to-tenant migration is not a formality. Get it wrong and you are reprocessing data, re-matching identities, or explaining to users why their mailbox landed in the wrong place. Here is how it has to sequence when you are working in Quest ODM. Identity first. Always. Before a single mailbox or OneDrive byte moves, source and target accounts need to be matched and provisioned correctly. ODM drives this through its directory sync and account matching logic. If that foundation is off, everything built on top of it is off. Coexistence second. Once identity is in order, you stand up GAL sync and free/busy sharing between the two tenants. This is what makes a phased migration survivable. Migrated users and not-yet-migrated users can still find each other and book meetings while waves run over days or weeks. Pre-seeding before cutover. ODM moves the bulk of mailbox and OneDrive data in advance, then runs incremental delta passes up to the cutover window. When cutover night arrives, you are finalizing deltas, not copying gigabytes from scratch. That is what keeps the window short and the risk contained. Data in dependency order last. Shared mailboxes, delegates, Teams, Groups, SharePoint. These have dependencies that break if you move them before the identities they rely on are in place in the target. Skipping steps or reordering them to hit an artificial deadline is usually where the expensive problems start.