Steps:

Set up a Migration Endpoint in the Source Tenant (old tenant).

Sign in to the Microsoft 365 Admin Center and navigate to Exchange Admin Center.

Set up a migration endpoint that connects to the source tenant.

Initiate the Migration:

Go to Recipients > Migration in the Exchange Admin Center.

Select Migrate to Exchange Online and choose the appropriate migration method (e.g., IMAP migration, Hybrid Exchange migration).

Complete the Migration:

After the migration completes, update the DNS records in the destination tenant to route emails to the new tenant.