Inventory the current service
List user mailboxes, shared addresses, aliases, forwarding rules, and applications that send messages. Include website forms, scanners, invoicing tools, and marketing services. Record how much historical mail must move and any business requirements for keeping records.
Identify the current provider and the people authorized to approve changes. Keep the old service available through verification rather than cancelling it as soon as new accounts are created.
Prepare the destination
Create the required accounts and access assignments. Confirm that users can sign in and recover access through the approved process. Plan shared addresses around their function; several people handling support mail need a clear workflow and appropriate permissions.
For messages sent to personal Gmail accounts, Google’s email sender guidelines provide current authentication and delivery requirements for the administrator to review.
Have the administrator obtain DNS values from the selected provider. Do not copy another company’s records. Mail-routing and domain-authentication changes need to account for every legitimate sending service.
Test a complete mail journey
Test inbound and outbound mail with an external address, replies, shared mailboxes, and attachments used in ordinary work. Test website forms and business applications separately. Confirm the expected historical messages are present and that users know where to find them.
Record unresolved items and the plan for retiring the old service. Keep a rollback decision point for a planned cutover rather than improvising during lost mail.
Finish the handoff
Document domain ownership, administrators, renewal responsibilities, and support contacts. Review employee onboarding and departure procedures. See Microsoft 365 services and email security to plan the ongoing setup.
Use NIST’s MFA guidance when reviewing ongoing protection for mailbox and administrator accounts as part of the handoff.