137 - Delete messages in mailbox

The easilst way is to empty root & users email message file
i.e. /var/spool/mail/root or /var/spool/mail/<username>.

There are two ways to delete all messages.

1.mail command & delete command :

Login linux as the user .

# mail

d 1-100     --> if you delete from 1 to 100,

2. Simply type the following command at shell :

 # cat /dev/null > /var/spool/mail/root

# cat /dev/null > /var/spool/user1

In Unix, Linux-like operating systems, /dev/null or the null device is a special file that discards all data written to it (but reports that the write operation succeeded),
and provides no data to any process that reads from it (yielding EOF immediately).