The following issue has been raised by multiple customers:

*User A sends and email from Outlook to User B and track the first email regarding an CRM Account "Microsoft"
*Open Sales > Accounts > Microsoft > Activities - the first email send to User B is tracked and visible
*User B replies to User's A first email
*Open Sales > Accounts > Microsoft > Activities - Email 1 is visible > Reply 1 is visible
*User A replies to User's B first reply
*Open Sales > Accounts > Microsoft > Activities - Email 1 is visible > Reply 1 is visible > Reply 2 is not there
*User B replies to user's A reply
*Open Sales > Accounts > Microsoft > Activities - Email 1 is visible > Reply 1 is visible > Reply 2 is not there > Reply 3 is visible
*If you open the entire communication by double click on the email in CRM, the entire communication is visible

User's personal settings are set: Email messages in response to Dynamics 365 email
Microsoft Dynamics CRM doesn't treat the emails send by User B as Dynamics emails and there doesn't track them in the Activities section of the selected account.
However, as i customer who select to track the entire communication in Dynamics CRM from the very first email with that external user, I'm expecting the entire communication to be tracked and each reply to be recorded as a separate activity for the account that it is "set regarding"

A lot of Dynamics users are communicating with clinets outside of the company or CRM in general. When decide to track the email with Dynamics App they would like to have a record of earch email send or received by this external user's to Dynamics CRM.