The UA-based CONNEG mechanism does query/response between two UAs that are
connected only by the store-and-forward email service. There is nothing
that dictates that application-level query/response exchanges be conducted
over connection-oriented, direct or real-time associations.
perhaps not, but once a message is relayed, the conversion (and the decision
of whether to deliver the message) is no longer under control of the sender -
actually the most likely scenario when using the conneg proposal with the
current infrastructure is that the message will be delivered, without
conversion, regardless of recipient capabilities.
I thought that this is what the fax people wanted to avoid?