einstein activity capture logs emails for people not in salesforce

If a Salesforce user sends an email to someone who is not a lead or contact via Outlook, the email is automatically logged in the activity timeline, and everyone with Salesforce access can see the email.  We don't know which addresses to exclude, as there could be thousands. How do you prevent the emails being logged for GDPR purposes?   Has anyone had this issue and found a way to resolve it?    Many thanks