Forum Moderators: not2easy
All those posts that are much longer than "me too" are copyrighted by the people that wrote them, with certain implied licenses granted by the act of posting.
With email lists, it really depends on who the owner is and what the terms are. If the owner of the list agrees to have it archived at your site, you are generally accepted to be in the clear. Though I am unaware if it has been tested in court.
Usenet (google groups) is a different story. The implied license is that it will be available on usenet. Google gets around this by making google groups a web based usenet client. They are not presenting themselves as an usenet archive. They are a web based client that allows you to read and post, with the interesting feature that they never expire messages.