Dave Yeo has released (1/13/2012) a test build of Enigmail 1.4pre, which should work with Thunderbird 8.0 and above, and SeaMonkey 2.5 and above. Also available (7/4/2010) is Enigmail version 1.1.2 for OS/2; this allows you to use GnuPG with your email in Thunderbird and/or Seamonkey. OS2World has a tutorial on setting it up.
Source: OS/2 Warp News and Rumors