Unfortunately, the first RC is bad. When I forked the DRUPAL-5 and DRUPAL-6--1 branches, I think I accidentally reverted. Anyway, RC2 should be good to go.
Bunch of stuff here.
-- You can manage mailing lists now.
-- The send mail form is smoothed out for forwards/backwards action.
-- Module now depends on mimemail
-- You can send a test email
-- You can define styles in your template and the mailout module will insert them inline. Define styles like normal css without class/id identifiers. Some docs need to be done on that.
-- All mailout stuff in under the Content menu now (admin/content)