acs-mail-lite now supports e-mail forwarding. Send an email to something like "malte#openacs.de \@ www.cognovis.de" and the system will forward the email to malte \@ openacs.de while tracking it in the mail tracking. Best of all, hitting the reply button will forward the reply again through the system so you are effectively tracking your whole communication with the user.
Drawback: The E-Mail might be easier classified as SPAM as the reply-to domain does not necessarily match your from_addr domain. On the other hand, the domain where the e-mail originates from is the same as the one in the reply-to.