Repeated content in e-mail messages

E-mail messages often contain boilerplate content of little interest. A more significant kind of duplicated inline content is when multiple bulletins remind the reader of some of the same stories or events that were already described in the previous digest. If one were to filter mail from such sources into specific folders then I can imagine that it might be both useful and feasible for a mail user agent add-on to display message content such that the blocks of lines that mirror those of recently preceding messages in that same folder are rendered less strongly.

(Or, better still, senders could assume that telling me once suffices.)