您的意思是在HTML版本的同时发送纯文本版本吗？

如果是我发现的this page 有助于设置：

关键在于：

 //create a boundary for the email. This 
 $boundary = uniqid(\'np\');

 //headers - specify your from email address and name here
 //and specify the boundary for the email
 $headers = "MIME-Version: 1.0\\r\\n";
 $headers .= "From: Your Name \\r\\n";
 $headers .= "To: ".$email."\\r\\n";
 $headers .= "Content-Type: multipart/alternative;boundary=" . $boundary . "\\r\\n";

 //Plain text body
 $message .= "Hello,\\nThis is a text email, the text/plain version.
 \\n\\nRegards,\\nYour Name";
 $message .= "\\r\\n\\r\\n--" . $boundary . "\\r\\n";
 $message .= "Content-type: text/html;charset=utf-8\\r\\n\\r\\n";

 //Html body
 $message .= "
  Hello,
 This is the html version.

 Regards,
 Your Name";
 $message .= "\\r\\n\\r\\n--" . $boundary . "--";