替换文件中的此代码
\系统\库电子邮件. php文件

public function subject($subject)
{
  $subject = $this->_prep_q_encoding($subject);
  $this->set_header('Subject', $subject);
  return $this;
}

结束日期

public function subject($subject)
{
   $subject = '=?UTF-8?B?'.base64_encode($subject).'?=';
   $this->_set_header('Subject', $subject);
   return $this;
}

并在电子邮件配置中设置电子邮件配置

$config = array(
    'protocol' => 'smtp',
    'charset' => 'utf-8',
    'newline' => "\r\n",
    'crlf' => "\n",
    'mailtype' => "html"
);