[exim] system mails not being delivered

hello,

messages sent to root are not being delivered.

Debian 3.1
exim4
2.4.27-2-686

$> ls -l /var/mail 
-rw-rw----  1 hans   mail     0 2005-10-20 15:18 tom
-rw-------  1 mail   mail  1019 2005-07-19 17:34 mail
-rw-rw----  1 root   mail     0 2005-10-28 09:29 root

$> cat /etc/aliases
root: real-tom

As user "tom":
$>echo $MAIL
/home/tom/Mail

Can anybody give me a hint what could be the reason for emails to root
not being delivered at all.

Thanks in anticipation.

Regards,


--
Realos