The general principle is that you track important emails as per Do you track important emails in CRM?
Microsoft Dynamics 365 allows users to track activities such as appointments, phone calls, emails, etc. This feature can be easily abused by users to record unrelated activities inside CRM. It is difficult sometimes to work out which type of activities should be recorded. These are the types of activities you should track in CRM:
Prerequisite: Install the CRM Add-in.
All sales activities should be tracked via CRM as an opportunity, company or contact.
Figure: This email should be tracked in CRM using the Add-in "Track without regarding"
By recording these activities, reports can be created to view:
Figure: Activities Report - Ulysses was the hardest worker for this month. Print this and put it on the wall and it will encourage everyone to log their calls
Note: You can see more details on what emails to track in Do you know to hit 'Track' when you receive an important email?