Download latest epel-release rpm from
http://download-ib01.fedoraproject.org/pub/epel/6/x86_64/
Install epel-release rpm:

rpm -Uvh epel-release*rpm

Install bsd-mailx rpm package:

yum install bsd-mailx

with mailx you can delete the messages as follow (as root):

bsd-mailx

…
& d *
& q