If you have a problem with the cron job/bounces/ can't send...

[xavier]

Hi,

These are installation issues. Could you post your question in the dedicated forum ?
http://forum.civicrm.org/index.php/board,21.0.html

If you upgraded from a previous version and the bounce processor doesn't work anymore, this is likely the new version of CiviCRM has uncover a previous configuration issue, and now is the time to fix it

Oh, and I'd like to suggest you this post http://forum.civicrm.org/index.php/topic,16430.0.html that is itself suggesting your to Read The Fantastic Manual chapter about how to configure CiviMail: http://book.civicrm.org/user/initial-set-up/email-system-configuration

Happy configuration!