使用 Xinetd 端口代理 Gmail 的 SMTP：
此法針對客戶端，Web 端請自己想辦法
yum install -y xinetd
cat /etc/xinetd.d/qqmail
service smtp-465
{
type = UNLISTED
port = 465
bind = 0.0.0.0
socket_type = stream
wait = no
user = nobody
redirect = smtp.exmail.qq.com 465
per_source = UNLIMITED
cps = 100 2
}
service smtp-587
{
type = UNLISTED
port = 587
bind = 0.0.0.0
socket_type = stream
wait = no
user = nobody
redirect = smtp.exmail.qq.com 587
per_source = UNLIMITED
cps = 100 2
}修改本地host指向代理即可通過客戶端發郵件：
xxx.xxx.xxx.xxx smtp.exmail.qq.com