Automate case creation from email inbox but no contact creation if unknown sender

Hello,

Calling D365 CRM experts! I have this requirement: We are creating cases from an email inbox, and in case the contact is in the database through its primary email, we associated it to the case. This is perfectly fine.

Problem is, this inbox has a lot of spam so we don't want to mess up the contact database with thrash records.  So the requirement is, if sender is not a CRM contact, only the case will be created. Is it any configuration available to get this done? I've gone through the documentation  and played with the two config settings - queue record creation and user preference email configuration - but no luck. 

Thanks a lot for any hint or help :)