There should be a flag on the Email table that indicates how the email got into CRM. Currently, Sales has 3 methods to push an email into CRM, 1) adding the "Tracked to Dynamics 365" category to their inbox email, 2) Dynamics 365 App for Outlook, and 3) Copilot for Sales.

it would be extremely helpful when tracking down email issues or email to case issues where/how the email(s) actually got into CRM.