Ruby has a built-in POP3 and IMAP library: http://www.rubycentral.com/book/lib_network.html#Net::POP.new http://rubymanual.org/class/Net%3A%3APOP3 http://rubymanual.org/class/Net%3A%3AIMAP
You could have them e-mail a "secret" e-mail address with a special subject line that indicates it's a blog entry (or to indicate category...whatever you want). Use those libraries to fetch the mail with a Ruby script, parse the message, and post the entry.
--Jeremy
