This is for a friend. He's looking for a simple PC E-Mail program that does two things. One, which most of them do, is to enable him to filter incoming mail and send different messages to different folders. The other, which I've never heard of, is a feature whereby a message is somehow marked or flagged once he writes a reply to it.
My e-mail program of choice is Forte Agent, and it's quite wonderful, especially in its handling of newsgroups. But I can't see that it does what my friend wants, which is to be able to look at a message he's received and say, "Oh, good. I already answered this." Does any program do this?