所以我有脚本发送纯文本和 html 的多部分电子邮件，由于某种原因纯文本版本不起作用，但是当我在 gmail 中显示原始内容时，我可以看到它正在发送。当我单击消息乱码时，它只显示html？
// headers
$headers = "MIME-Version: 1.0\r\n";
$headers .= 'From: From Name <'. FROM_EMAIL. ">\r\n";
$headers .= 'To: '.$member->member_info['memem']. "\r\n";
$headers .= 'Bcc: receipts@gmail.com' . "\r\n";
$headers .= "Subject: Registration Receipt\r\n";
$headers .= "Content-Type: multipart/alternative;boundary=" . $boundary . "\r\n";
// Additional headers
$message . "\r\n\r\n--" . $boundary . "\r\n";
$message .= "Content-type: text/plain;charset=utf-8\r\n\r\n";
$message .= $receipt_txt;//plain text
$message .= "\r\n\r\n--" . $boundary . "\r\n";
$message .= "Content-type: text/html;charset=utf-8\r\n\r\n";
$message .= $receipt_html;//html
$message .= "\r\n\r\n--" . $boundary . "--";
mail( $member->member_info['memem'], 'Registration Receipt', $message, $headers );