It also limits the ability of an external party that has been
delegated a key for a particular service to (mis)use that key for
other, unauthorized services.
That's probably the best reason for it. In any event, this is surely
moot at this stage. Most protocols end up with unused or under-used
parts to them. It's a pity my Mum never warned me that protocol
design has much to do with prophesying.
Mark.
_______________________________________________
NOTE WELL: This list operates according to
http://mipassoc.org/dkim/ietf-list-rules.html