Having pondered the layer thing some more, it occurs to me that we have several decades of practice with software that validates the format of mail messages to a greater or lesser extent, with the emphasis on lesser. Different software depends on different bits of the message to be correct, which means that some leakage of the message validation into different applications is unavoidable unless you're willing to lose mail that has flaws that don't matter to the applications that it passes through.
In procmail, for example, doubled subjects only matter if you have a rule that does something depending on the subject line. In MUAs, based on the random way existing MUAs handle them, they don't matter at all. So that's where my SHOULD NOT comes from. It leaks the bit that matters to DKIM. Regards, John Levine, [email protected], Primary Perpetrator of "The Internet for Dummies", Please consider the environment before reading this e-mail. http://jl.ly _______________________________________________ NOTE WELL: This list operates according to http://mipassoc.org/dkim/ietf-list-rules.html
