Moving from an on-premise Exchange server to Exchange Online, and from a file server to OneDrive/SharePoint — the most common cloud-migration scenario for a mid-sized company. Done right, it's completed in 4-8 weeks; planned wrong, it takes months.
01. Preparation
First steps: license planning, DNS management, identity synchronization (Entra ID Connect), data classification. No data migration should start before these are done.
02. User Identities
Accounts in Active Directory need to be synchronized with Entra ID (formerly Azure AD). This step is the most critical; wrong matching causes users to lose access.
03. Exchange Migration
Cutover (small scale, all at once), staged (mid-scale, gradual) or hybrid (large scale, complex) migration options. Each has different prerequisites and a different time plan.
04. File Migration
Moving from an on-premise file server to OneDrive/SharePoint: the SharePoint Migration Tool (SPMT) or third-party tools. Folder structure and permissions must be moved correctly; an opportunity for redesign.
05. User Training
Even if the technical migration succeeds, user resistance can slow the project. At least a week of training, short videos and an FAQ list should be prepared.
06. After Cutover
Don't shut down the on-premise systems immediately after migration. Run them in parallel for 2-4 weeks; keep a fallback path ready for critical problems.