For the ones that refer to things that are theoretically real, verifiable, events, I typically look them up in Snopes, look further for primary sources if possible, and reply back with polite (I hope) corrections. (The ones that contain jokes, or lists of palindromes, or cute animated pictures of puppies, I just delete.) My grandfather has never responded to my replies, although I've occasionally gotten email from other family members about it.
This week, however, my grandfather has sent me a pair of emails saying things that Snopes actually verified to be true! I don't know what to make of this development.
[item the first] [item the second]