Load Balance SMTP for Exchange 2007 relay

True, the rfc lays the framework, but how many implementations are there that won't require legwork? My point was x-forwarded-for is well-supported in http implementations, but not so much with smtp. There have been enough questions on this front that it might be worthwhile to try to get a working solution with sendmail and Exchange and look at LTM implementations with stream or an smtp proxy.