Do I need to archive messages for all mailboxes at a domain?

When the Archive service is enabled, or at any time subsequent to that, administrators can choose whether the archive is enabled for all mailboxes, or for selected mailboxes only. The default, and the recommended option, is to simply archive all mailboxes, so that administrators do not need to add or remove mailboxes for the Archive service on an ongoing basis.

Industry compliance requirements may require all mailboxes of the domain maintain archive messages. Check with your particular compliance requirements.