Exchange to Google Workspace migration

Mail transfer from Exchange is fast and well supported. What extends the project is everything else the server does: it relays mail for scanners and line-of-business applications, it holds public folders, it backs resource mailboxes for rooms and equipment, and it is frequently the only thing that knows why a particular distribution list exists.

We inventory those dependencies first. Each one gets a destination, an owner and a decommissioning date, and the mailbox migration proceeds against that plan rather than in front of it.

Most organisations keep Active Directory and synchronise identity into Google Workspace with Google Cloud Directory Sync, because domain-joined machines and internal applications still depend on it. That is a supported end state, not a compromise, and it means the migration does not have to solve identity at the same time as mail.

Where the intention is to retire the domain entirely, we treat that as a separate phase after mail is stable. Combining a mail migration with a directory retirement doubles the failure surface for no scheduling benefit.

Public folders are the headline case, but there are others: mailbox-level retention tags, in-place holds tied to Exchange itself, and elaborate transport rules that assume Exchange semantics. Google Vault covers retention and legal hold well, but it is a different model, and mapping to it is a decision rather than a translation.

We list every such object in discovery with the closest Google equivalent, what is lost, and what it would cost to preserve. That list is signed off before the first mailbox moves, which is why our Exchange projects rarely produce surprises in week five.

Estates above roughly 100 mailboxes move by department, with coexistence in between: mail routes correctly between migrated and unmigrated users, and free-busy lookup works across the boundary. That keeps the blast radius of any single weekend small, and it lets the pilot group's experience shape the runbook for everyone else.

Once the last department is across, the Exchange server is put into receive-only mode for an agreed period, then shut down and retained as an offline image rather than deleted immediately.