centos 5.9 无法安装sendmail

YCYCC

[root@test ~]# yum install sendmail sendmail-*
Loaded plugins: fastestmirror, security
Loading mirror speeds from cached hostfile
* base: mirror.oss.ou.edu
* extras: mirror.rackspace.com
* updates: mirror.clarkson.edu
Excluding Packages in global exclude list
Finished
Setting up Install Process
No package sendmail available.
No package sendmail-* available.
Nothing to do

请给个解决方法，谢谢基友