Extmail相关依赖包：courier-authlib-0.66.2.tar.b2,courier-unicode-1.2.tar.bz2,libtool-ltdl-devel-2.4.2-22.el7_3.x86_64.rpm,mailx-12.5-19.el7.x86_64.rpm,mysql-5.7.32-linux-glibc2.12-x86_64.tar.gz,postfix-3.0.11.tar.gz,Unix-Syslog-1.1.tar.gz