I find Eric's comment "sendmail took the approach that it should try to accept, clean up, and deliver even very 'crufty' messages instead of rejecting them because they didn't meet some protocol" (from http://www.busan.edu/~nic/networking/sendmail/prf1_03.htm ) somewhat ironic given that any time I screw up a sendmail configuration the end result is mail disappearing without trace

Thankfully I only have to touch sendmail config files about once every 18 months (which probably also explains why I screw it up every time), in between times it just keeps working...