ExchangeOnline offers options that can assist during a merger or acquisition process between two organizations. These options include:
Migrating both organizations to ExchangeOnline, while creating new email accounts and maintaining the old ones.
Keeping one organization in its onpremise environment and moving the other organization to Exchangeonline separately.
Keeping one organization in its onpremise environment and moving the other organization to
ExchangeOnline in a hybrid Exchange arrangement, then onboarding the other organization to onpremise before decommissioning Exchange Online.
Setting up hybrid Exchange and moving users from both organizations either to on-premise or
Exchange Online as their job function dictates.