By default, Truly attempts to match a tracked email to a Contact or Lead.
Matching Logic
It implements the following logic to handle the many edge cases in Salesforce:
If the email matches Contacts and Leads, Contacts are prioritized
If duplicate Contact/Leads exist, Truly will attempt to find the one owned by the user on behalf of whom the email is being logged.
If the user owns duplicate entities, the most recently updated will be chosen.