SBBSecho doesn't import SEEN-BYs from echomail messages without tear or origin lines
FTS-4 just says "seen-by lines at the end of Conference Mail messages", so we probably should be parsing these even if/when there is no origin line.
FTS-4 just says "seen-by lines at the end of Conference Mail messages", so we probably should be parsing these even if/when there is no origin line.