Hi @S.N Soerdjbali ,
Per my understanding, the official recommended tool for cloud-to-cloud migration between SharePoint Online is Mover, please check this official link for more information:
Mover Cloud Migration
In fact, we are currently providing technical support for SharePoint and mail migration is more related to exchange, so for the part of migrating mails, I have found a relevant article for you:
How to migrate mailboxes from one Microsoft 365 or Office 365 organization to another
You could post a new thread with the tag for more help about mail migration.
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