Delete / Remove User Account : Error : Creating mailbox file: File exists

[root@test ~]# /usr/sbin/useradd -g oinstall -G dba,oper oracle
Creating mailbox file: File exists
[root@test ~]#

[root@test mail]# pwd
/var/spool/mail

delete oracle file

[root@test mail]# ls -lrt
total 0
-rw-rw----. 1 rpc   mail 0 Feb 21 22:12 rpc
-rw-rw----. 1 54321 mail 0 Feb 22 00:26 oracle
[root@test mail]#
[root@test mail]# cat oracle
[root@test mail]#
[root@test mail]# rm -rf oracle
[root@test mail]#
[root@test mail]# userdel -r oracle
[root@test mail]# /usr/sbin/useradd -g oinstall -G dba,oper oracle
[root@test mail]#