email tracking scenario?

Hello - I have the following email tracking scenario:

1. Person sends an email to me at me@company.com
2. CRM creates new contact from email address
3. CRM creates new case for new contact
4. CRM associates the original email with the case
5. CRM sends an auto-response email

So if the original auto-response email has been configured with a From address of the PM assigned to the case and the contact replies to that email then the contact's email response will be sent directly to the email address associated with the Case PM.

In this scenario if I go to case activities then the last email sent from the contact won't be reflected in the Activities list.  If the case PM transfers the case to a different PM then this last email from the contact could get lost, the new Case PM wouldn't know about it.

So how do you go about managing this scenario?  Is there a  process, setting or configuration that I can use to effectively group the last email from the contact with the related case emails?