It's interesting that freecycling has ended up becoming quite a learning adventure into the proper application of intellectual property laws and rights.
Many get easily confused about what trademarks vs patents vs copyrights are really about. Used properly these are all good things that allow our economy and society to function better. That's why they were invented. But misused or misunderstood, they can lead to much pain and abuse and injustice.
In general trademarks, patents, and copyright are all intended to protect "profits" in use in commerce and should never be used to control free speech -- although some misguided corporations and individuals keep trying to do this.
On the trademark front we've proven this a couple of times thanks to the Ninth Circuit Court of Appeals. See http://freecycleforever.org/history/ to read more on the trademark front.
On the copyright front we have not had any lawsuits (and I hope we won't), but here is an important point for all:
When replying to an email it is OK (in terms of copyright) to include the entire previous email (and even email chain) that is relevant to your reply.
It may not be good etiquette because this may make the email rather large and clog the digest version of an email list. It may also confuse your audience because people may not know exactly what point you are replying to. However from a legal standpoint it should be just fine because you are engaged in free speech -- debate with give and take. The discussion is enabled by including prior emails for reference.
I know that others have raised "copyright" as a reason that entire emails should not be included in reply emails, but this is not correct in so far as I've been able to determine as long as the intent is to enable discussion and not to reproduce a work to deny someone else from getting compensation for that work.
Including entire previous emails in replies is:
1) common -- billions of people do it daily.
2) easy -- most email programs do this automatically and it takes work to prevent.
3) appropriate -- so that the points and counter points can all be read in context to see if they are really logical or not.
4) expected -- so that debates are not just one sided, you need multiple points of view to understand the different points -- there are multiple sides to every discussion.
This is all protected by the "fair use" doctrine in addition to not being commercial speech but rather free speech. By commercial speech I mean communication that is intended to earn money in some direct way -- like in advertising or publishing. Even in commercial speech "fair use" can protect someone that is quoting another.
In contrast, if you use someone else's material in a way that harms the commercial value of the work -- for instance republishing large sections of material that someone would otherwise have to buy. This is most likely a copyright violation that is not protected by the "fair use" doctrine. The original author was generally paid money to create the work and thus it is in turn sold to recoup this cost as well as make a profit on it so the author and others involved can make a living.
Law can be a tricky and complicated area but hopefully this explanation makes sense to most people.
Please note that I am not a lawyer and I'm not giving you professional legal advice. However this does not block me from discussing such situations or you from coming to reasonable conclusions based on the information presented.
For references, please see:
1) "My posting was just fair use!" at http://www.templetons.com/brad/copymyths.html