We are in the process of moving from onsite Exchange to G-Suite for email. In the past we bounced all external email through Gmail before it hit our Exchange server as a backup and spam filter. As a result, everyone's Gmail inboxes are loaded with external emails and they are all unread.
Before I move all users to Gmail I would like to clear out all those emails for all staff, so they get a fresh inbox. Is there a way I can do this without logging into everyone's accounts? I have well over 100 accounts to clear.