Why not post a message on your Site News forum? Just be sure to check that the setting 'Force everyone to be subscribed' is selected.
Alternatively, you could use Michael Penney's excellent Quickmail Block - see http://moodle.org/mod/forum/discuss.php?d=18117 for more info. You can get that block at CVS/contrib/quickmail, or download the zip file at http://moodle.org/download.php/modules/quickmail.zip
Alternatively, you could use Michael Penney's excellent Quickmail Block - see http://moodle.org/mod/forum/discuss.php?d=18117 for more info. You can get that block at CVS/contrib/quickmail, or download the zip file at http://moodle.org/download.php/modules/quickmail.zip