Matching Parent Emails with the Document Identifier
When setting up an analytics profile for email threading in Relativity, be sure that the Parent document ID field will match the document identifier of the parent email.
Failing to do will cause errors in email threading. When you view the metadata you should see a match like this:
If the Parent Document ID is not set for the email itself, email threading will still generate valid results. If you find the 'Parent Document ID' field set to something other than the document identifier (the field on the left with a link to the viewer) it is a sign that the admin has not performed email threading correctly.