/**
 * 功能：邮件发送函数
 * @param string $to 目标邮箱
 * @param string $subject 邮件主题（标题）
 * @param string $to 邮件内容
 * @return bool true
 */
 function sendMail($to, $subject, $content) {
 vendor('PHPMailer.class#smtp'); 
 vendor('PHPMailer.class#phpmailer'); //注意这里的大小写哦，不然会出现找不到类，PHPMailer是文件夹名字，class#phpmailer就代表class.phpmailer.php文件名
 $mail = new PHPMailer();
 // 装配邮件服务器
 if (C('MAIL_SMTP')) {
  $mail->IsSMTP();
 }
 $mail->Host = C('MAIL_HOST'); //这里的参数解释见下面的配置信息注释
 $mail->SMTPAuth = C('MAIL_SMTPAUTH'); 
 $mail->Username = C('MAIL_USERNAME');
 $mail->Password = C('MAIL_PASSWORD');
 $mail->SMTPSecure = C('MAIL_SECURE');
 $mail->CharSet = C('MAIL_CHARSET');
 // 装配邮件头信息
 $mail->From = C('MAIL_USERNAME');
 $mail->AddAddress($to);
 $mail->FromName = C('MAIL_FROMNAME');
 $mail->IsHTML(C('MAIL_ISHTML'));
 // 装配邮件正文信息
 $mail->Subject = $subject;
 $mail->Body = $content;
 // 发送邮件
 if (!$mail->Send()) {
  return FALSE;
 } else {
  return TRUE;
 }
 }

<?php
 return array(
 //其他配置项省略......
 // 配置邮件发送服务器
 'MAIL_SMTP'   => TRUE,
 'MAIL_HOST'   => 'smtp.163.com',   //邮件发送SMTP服务器
 'MAIL_SMTPAUTH' => TRUE,
 'MAIL_USERNAME' => '123***@163.com',  //SMTP服务器登陆用户名
 'MAIL_PASSWORD' => '123456abc',    //SMTP服务器登陆密码
 'MAIL_SECURE'   => 'tls',
 'MAIL_CHARSET'  => 'utf-8',
 'MAIL_ISHTML'   => TRUE,
 'MAIL_FROMNAME' => '某某网站客户',
 );

<?php
 namespace Home\Controller;
 use Think\Controller;
 class IndexController extends Controller {
 public function index(){
  
 }
 public function send(){
  if(sendMail('vsiryxm@qq.com','你好!邮件标题','这是一篇测试邮件正文！')){
   echo '发送成功！';
  }
  else{
   echo '发送失败！';
  }
 }
 }