email tracking token question?

Hello - I know when you turn on email tracking in CRM it appends a token to the end of the subject like "CRM: 0001001"

Is the tracking token stored in any other way in the email?  For example, in some type of header or metadata?  Or if a contact removes the token from the subject line then has the token essentially been completely removed from the email?

Also, do you know the underlying datastore where this token is stored/incremented?  Is it a SQL Server table or some other type of structure?