sendmail -f 可以指定发件人的邮箱， -t 可以指定收件人的邮箱。这里先把一封邮件准备好，名字是 a.txt。
# a.txt
From: TEST <test@youxiangmi.com>
To: senlin <youxiangmi.com@qq.com>
MIME-Version: 1.0
Content-type: text/html
Subject: mail test
Test Content
sendmail指定发件人地址
cat a.txt | sendmail -f test@youxiangmi.com -t youxiangmi.com@qq.com
#!/bin/bash
cat << EOF | sendmail -f test@youxaingmi.com -t youxiangmi.com@qq.com
From: TEST <test@youxaingmi.com>
To: yxm <youxiangmi.com@qq.com>
MIME-Version: 1.0
Content-type: text/html
Subject: hello
this is mail
EOF