Internal emails are being tracked in Dynamics 365

I have the following issue which I can't seem to solve...

• User A sends an email to user B, which is automatically, (= no manual interference by one or the other party), tracked in Dynamics 365
• However, this is an internal email and thus should not be tracked into Dynamics
• When I check the tracked email, it shows "From" = User A and "To" = User B

I've already checked the following settings and scenario:

Personal settings - email settings:

• User A:
  • Track email messages = email messages from CRM Leads, Contacts and Accounts
  • Create records = NO
• User B:
  • Track email messages = email messages from CRM Leads, Contacts and Accounts
  • Create records = NO

System settings - tab "email":

• Configure folder-level tracking and email correlation:
  • folder-level tracking = OFF
  • Correlation to track email conversations = OFF
• Set tracking options for emails between Microsoft Dynamics 365 users
  • Track emails sent between Dynamics 365 users as two activities = ON

Scenario's

• Scenario A: User A is also a contact and thus, the systems tracks him
  • NOT POSSIBLE: User A is not a contact, moreover, I have the same issue with other users who are also no contacts.
• Scenario B: this is due to "relationship insights" (proposed by Nelson Johnson in this post)
  • NOT POSSIBLE: relationship insights isn't even activated in the system.
• Scenario C: User A is being linked to the system by the Dynamics 365 for Outlook app, through the Address Book (suggested by Microsoft docs)
  • NOT POSSIBLE: as user A is not in the D365 for Outlook app-address book of user B.
• Scenario D: the system magically knows who is user A and user B in the system and thus links the email to both users
  • NOT POSSIBLE: the email address for user A in D365 is an "@domain.onmicrosoft.com" address and thus the system shouldn't be able to link them.
  • Sidenote: I noticed a new read-only field which is called "user name" (domain name), and seems to be synchronized with O365 and has the "@domain" address.

Final thoughts:

In the Microsoft documentation, it states

"When Dynamics 365 for Customer Engagement apps tracks an email, it associates the email address to a record within Dynamics 365 for Customer Engagement. The contents of the email From field can only be associated with one Dynamics 365 for Customer Engagement apps record. If there are duplicate records within Dynamics 365 for Customer Engagement apps with the same email address, the contents of the email From field will resolve to the first active record in the following order:

1. SystemUser
2. Contact
3. Account
4. Lead"

So I interpret this "WHEN" as in "WHEN the system tracks" an email. However, the system should simply not track the specific mails I was talking about as it was between users and no contacts were involved. Which leads me to the question "Is internal tracking something that can not be prevented?" TopCat and KittenFace posted in 2014 already a workaround to delete internal emails, but I'm wondering if this is still the case...