> "From" lines and "Reply-to" and whatever are headers that are meant to > be processed by computers. So, you can say all you want about how > dumb MUAs do or do not process these (and how intermediate mail > servers should keep their mits off). Now, humans use these lines, > too. So, call them dual use. > > The subject line, on the other hand, is just for people. Book titles are for people, too. Does that mean that it's okay for a bookseller or library to change the titles on books, in order to help the consumer indentify where they came from? I'm a bit surprised at the frequency at which people who claim to be networking protocol engineers fail to appreciate the benefits of clean separation-of-function and layering.