The mailhub seems to be a good place to think about.
Leave a "tail -f /var/log/mail/current" running in a shell while you wait for a cron to be executed. When it runs, check out what happens in the logfile.
Regards,
Saffi
--
Ricardo Saffi Marques
Laboratório de Administração e Segurança de Sistemas (LAS/IC)
Universidade Estadual de Campinas (UNICAMP)
Cell: +55 (19) 8128-0435
Skype: ricardo_saffi_marques
Website: http://www.rsaffi.com