How to Use Microsoft 365 Compliance Search Purge Actions to Remove Exchange Online Messages
Office 365 content searches now support a hard-delete (permanent deletion) option for the purge action, but only for mailbox items. You can purge up to 10 items at a go. If you have more to purge, you just have to keep on purging until everything is gone. Or use the Search-Mailbox cmdlet, which keeps on proving its usefulness to administrators who need to remove lots of mailbox items quickly.