Where does sent and received email go in relation to a contact. I.e how does the owner of the business see the email history between his client and his employee?
Directly in OpenERP you can find all messages when you activate the "technical features" setting for the account you want to use (logout/login after) and then go to Settings --> Technical --> Email --> Messages. There you can also sort for sender or whatever parameter you want to filter. You will see all sent and received messages.
Depending on your email setup for OpenERP you may have configured one catchall email address that is used for all OpenERP related messaging. Take a look into this accounts INBOX to find all messages or notifications about new messages. But the amount of emails found in this account really depends on your overall setup. As far as I could find out sent messages are not stored in the SENT folder of this email account.