I check my journctl. I did "journalctl -u bacula-dir.service", now it show a different error says'
Aug 15 23:56:17 thidwick bacula-dir[5858]: 15-Aug 23:56 Message delivery ERROR: Mail program terminated in error.
CMD=/usr/lib/bacula/bsmtp -h localhost -f "(Bacula) <root@localhost>" -s "Bacula: Backup OK of thidwick-fd Incremental" root@localhost
ERR=No such file or directory
Maybe, this will give you guys more hint on the actual problem?
Thanks,
Jing