Someone asked me -- is it a copyright infringement to forward off-list (say, to some friends, or to another discussion list) a message that has been posted to a large (say, 200-member) and open-for-subscription discussion list? Here's a quick analysis.
E-mail, like nearly all writing (including things written on a blackboard or a cocktail napkin, if they're more than just a few words), is automatically copyrighted. You don't need to put a copyright notice on it, and you don't need to register it anywhere. If someone asks you "What do I need to do copyright this?" (where "this" is something of even modest complexity, beyond just a few squiggles or several words), the answer is "Write it down."
But there are two ways in which forwarding or other copying of a messages may nonetheless not be infringement. First is if the writer conveys an implied license to make copies -- if the writer acts in a way that a reasonable reader would interpret as voluntarily permitting others to copy.
A classic example from the real world is if someone sends a letter to the editor of a newspaper that starts with "Dear Editor:." Is the letter protected by copyright? Sure, it's written down. Would publishing it be copying? You bet. But a reasonable publisher would interpret the writer's conduct as authorizing (here, even requesting) that the letter be copied. Likewise, copying a sender's message when replying to the whole list is almost certainly implicitly licensed; the same is true of copying the message to a separate folder on your computer, or printing it out for your physical files.
I suspect that forwarding off-list is generally not implicitly licensed, because there's not the same kind of well-established understanding that this is fine -- but it's impossible to tell for sure, since this doctrine is quite vague, and since to my knowledge there've been no published court opinions applying it in this context (nearly no-one sues over such things).
Note that implied licenses can always be disclaimed by a prominent notation on the writer's part. A letter to an editor that says "Dear Editor: This is not for publication, but I wanted to tell you that . . ." does not implicitly license the editor to publish the letter, since a reasonable editor wouldn't think that the author agrees to have the letter be published. Likewise with an e-mail that starts with "NOT FOR FORWARDING." (Fair use claims, see below, can still be made despite such a notation, but not implied license claims).
Second, forwarding (to an off-list friend or to another list) a message posted on a discussion list may well be a fair use. This is especially so if the purpose of the copying is commentary or criticism of the message ("Look what a horrible argument I saw being made on a list I'm on : . . . Here's why it's horrible [point-by-point rebuttal follows]."), but it's probably even so if the purpose is simply to pass along something that's interesting.
The forwarding is noncommercial; the item has probably been published, because it has been distributed to a large group of people; the item is probably mostly factual rather than creative writing (unless it's a list for posting one's short stories or some such); and, most importantly, there's virtually no effect on the value of or market for the work, since there's no market for the work in the first place. If one is forwarding the entire e-mail, that cuts against fair use; but on balance, I think there'd be a credible fair use claim in any event. Again, though, since there've been no reported cases on the subject, it's impossible to tell whether such off-list forwarding would be fair use.
Note, though, that if you change the facts slightly, both these analyses may end up being different. If the list is small, then the post might be seen as unpublished, and the fair use claim would be much weaker. If the item is reprinted or reposted in a commercial place (such as a newspaper), then the fair use claim would again be weaker. My analysis above is limited to a specific scenario: Noncommercial forwarding of a message posted to a fairly large and open list.