1.mail -s "Title“ 123456@163.com 只有主题，没有内容
2. 有邮件内容
echo "text" | mail -s "Title" 123456@163.com
cat file.txt | mail -s "Title" 123456@163.com
mail -s "Title" 123456@163.com < file.txt
3.向多个地址发送邮件
echo "send multiple mails" | mail -s "Multi" 123456@163.com,654321@163.com,321456@163.com