我想在 CentOS 6 上安装 postfix，但出现以下错误：
yum install postfix -y
Loaded plugins: fastestmirror
Setting up Install Process
Determining fastest mirrors
YumRepo Error: All mirror URLs are not using ftp, http[s] or file.
Eg. Invalid release/repo/arch combination/
removing mirrorlist with no valid mirrors: /var/cache/yum/x86_64/6/base/mirrorlist.txt
Error: Cannot find a valid baseurl for repo: base
谁能告诉我如何解决这个问题？这与人们说 CentOS 6 已死有关系吗？有什么解决办法吗？