Practical guide. Use only the connection and DNS details provided when your account is activated; .example domains are illustrative.
Create an inventory
Inventory people, mailboxes, aliases and domains. Note the approximate email volume and who can authorize access to the source provider.
Define what moves
List messages, folders, contacts, calendars, rules and permissions separately. Confirm each item, keep a backup or recovery route and agree responsibilities.
Plan tests and recovery
Do not cancel the previous service or change MX records before agreeing a plan. Define sending and receiving checks, a recovery path and when outstanding data will be reviewed.