In an article on Copyright on the Internet, Thomas G. Field, at the
Franklin Pierce Law Center, writes about licenses implied in fact for
emails and web site posts.
http://www.fplc.edu/tfield/copyNet.htm
This same topic is mentioned in an article in the Cyberspace
Law Insitute and Counsel Connect section on Cyberspace Law for
Non-Lawyers article "Copyright Law in Cyberspace"
http://nat-www.uia.ac.be/u/hansver/cyberlaw/copyright.html