I have a qmail server, which cannot be changed into anything else, because it is part of a much larger system. It should route all emails to a Zarafa server, which only uses the LMTP protocol and to which I don't have physical access.
How is it possible to make qmail deliver the emails to the LMTP server?
I don't see any indication that qmail supports LMTP. Could you redirect to an exim process which runs the LMTP delivery. This could be configured as a pipe delivery target. Alternatively, exim could run on another port or server.