On Mon, 14 May 2012 08:25:03 -0800, Kevin Miller
Last I heard Outlook Express (or whatever they call it now) didn't
support yEnc, but Thunderbird has for a long time.

As far as I know, Outlook Express (or Outlook for that matter) still
doesn't support yEnc. However, there are a number of add ons that
enable those two mail readers to do so. yproxy is one of the more
popular.
http://www.yproxy.com/