saving the email of a mail merge document to a contact record

saving the email of a mail merge document to a contact record

I've created a mail merge template and an email along with it. I have successfully created a Workflow to execute the mail merge and send the email. However, it doesn't save the email to the contact record. Does anyone know how o make this work? My client needs to have a record of the sent email connected to the contact without doing it manually.