工作理念:

if (isset($_POST['submit'])) {
    $mailto = $_POST["mailTo"];
    $from_mail = $_POST["fromEmail"];
    $replyto = $_POST["fromEmail"];
    $from_name = $_POST["fromName"];
    $message = $_POST["message"];
    $subject = $_POST["subject"];

    $filename = $_FILES["fileAttach"]["name"];
    $content = chunk_split(base64_encode(file_get_contents($_FILES["fileAttach"]["tmp_name"])));

    $uid = md5(uniqid(time()));
    $name = basename($file);
    $header = "From: " . $from_name . " <" . $from_mail . ">\r\n";
    $header .= "Reply-To: " . $replyto . "\r\n";

    $header .= "MIME-Version: 1.0\r\n";
    $header .= "Content-Type: multipart/mixed; boundary=\"" . $uid . "\"\r\n\r\n";
    $header .= "This is a multi-part message in MIME format.\r\n";
    $header .= "--" . $uid . "\r\n";

// You add html "Content-type: text/html; charset=utf-8\n" or for Text "Content-type:text/plain; charset=iso-8859-1\r\n" by I.khan
    $header .= "Content-type:text/html; charset=utf-8\n";
    $header .= "Content-Transfer-Encoding: 7bit\r\n\r\n";

// User Message you can add HTML if You Selected HTML content
    $header .= "<div style='color: red'>" . $message . "</div>\r\n\r\n";

    $header .= "--" . $uid . "\r\n";
    $header .= "Content-Type: application/octet-stream; name=\"" . $filename . "\"\r\n"; // use different content types here
    $header .= "Content-Transfer-Encoding: base64\r\n";
    $header .= "Content-Disposition: attachment; filename=\"" . $filename . "\"\r\n\r\n"; // For Attachment
    $header .= $content . "\r\n\r\n";
    $header .= "--" . $uid . "--";
    if (mail($mailto, $subject, "", $header)) {
        echo "<script>alert('Success');</script>"; // or use booleans here
    } else {
        echo "<script>alert('Failed');</script>";
    }
}

要发送带有附件的电子邮件，我们需要使用multipart/mixed MIME类型，该类型指定混合类型将包含在电子邮件中。此外，我们希望使用多部分/替代MIME类型来发送纯文本和HTML版本的电子邮件。看一下这个例子:

<?php 
//define the receiver of the email 
$to = 'youraddress@example.com'; 
//define the subject of the email 
$subject = 'Test email with attachment'; 
//create a boundary string. It must be unique 
//so we use the MD5 algorithm to generate a random hash 
$random_hash = md5(date('r', time())); 
//define the headers we want passed. Note that they are separated with \r\n 
$headers = "From: webmaster@example.com\r\nReply-To: webmaster@example.com"; 
//add boundary string and mime type specification 
$headers .= "\r\nContent-Type: multipart/mixed; boundary=\"PHP-mixed-".$random_hash."\""; 
//read the atachment file contents into a string,
//encode it with MIME base64,
//and split it into smaller chunks
$attachment = chunk_split(base64_encode(file_get_contents('attachment.zip'))); 
//define the body of the message. 
ob_start(); //Turn on output buffering 
?> 
--PHP-mixed-<?php echo $random_hash; ?>  
Content-Type: multipart/alternative; boundary="PHP-alt-<?php echo $random_hash; ?>" 

--PHP-alt-<?php echo $random_hash; ?>  
Content-Type: text/plain; charset="iso-8859-1" 
Content-Transfer-Encoding: 7bit

Hello World!!! 
This is simple text email message. 

--PHP-alt-<?php echo $random_hash; ?>  
Content-Type: text/html; charset="iso-8859-1" 
Content-Transfer-Encoding: 7bit

<h2>Hello World!</h2> 
<p>This is something with <b>HTML</b> formatting.</p> 

--PHP-alt-<?php echo $random_hash; ?>-- 

--PHP-mixed-<?php echo $random_hash; ?>  
Content-Type: application/zip; name="attachment.zip"  
Content-Transfer-Encoding: base64  
Content-Disposition: attachment  

<?php echo $attachment; ?> 
--PHP-mixed-<?php echo $random_hash; ?>-- 

<?php 
//copy current buffer contents into $message variable and delete current output buffer 
$message = ob_get_clean(); 
//send the email 
$mail_sent = @mail( $to, $subject, $message, $headers ); 
//if the message is sent successfully print "Mail sent". Otherwise print "Mail failed" 
echo $mail_sent ? "Mail sent" : "Mail failed"; 
?>

正如你所看到的，发送带有附件的电子邮件很容易完成。在前面的例子中，我们有多部分/混合MIME类型，在里面我们有多部分/替代MIME类型，指定两个版本的电子邮件。为了将附件包含到消息中，我们将指定文件中的数据读入一个字符串，使用base64对其进行编码，将其分割为更小的块，以确保它与MIME规范匹配，然后将其作为附件包含。

从这里拍的。

Swiftmailer是另一个易于使用的脚本，可以自动防止电子邮件注入，使附件变得轻而易举。我也强烈反对使用PHP内置的mail()函数。

使用方法:

下载Swiftmailer，并将lib文件夹放在你的项目中 使用require_once 'lib/swift_required.php'包含主文件;

现在当你需要邮寄时添加代码:

// Create the message
$message = Swift_Message::newInstance()
    ->setSubject('Your subject')
    ->setFrom(array('webmaster@mysite.com' => 'Web Master'))
    ->setTo(array('receiver@example.com'))
    ->setBody('Here is the message itself')
    ->attach(Swift_Attachment::fromPath('myPDF.pdf'));

//send the message          
$mailer->send($message);

更多信息和选项可以在Swiftmailer文档中找到。

我同意评论中的@MihaiIorga -使用PHPMailer脚本。听起来你拒绝是因为你想要更简单的选择。相信我，比起自己使用PHP内置的mail()函数，PHPMailer是一个更简单的选择。PHP的mail()函数真的不是很好。

使用PHPMailer:

下载PHPMailer脚本:http://github.com/PHPMailer/PHPMailer 提取归档文件并将脚本文件夹复制到项目中方便的位置。 包括主脚本文件——require_once('path/to/file/class.phpmailer.php');

现在，发送带有附件的电子邮件从异常困难变得异常简单:

use PHPMailer\PHPMailer\PHPMailer;
use PHPMailer\PHPMailer\Exception;

$email = new PHPMailer();
$email->SetFrom('you@example.com', 'Your Name'); //Name is optional
$email->Subject   = 'Message Subject';
$email->Body      = $bodytext;
$email->AddAddress( 'destinationaddress@example.com' );

$file_to_attach = 'PATH_OF_YOUR_FILE_HERE';

$email->AddAttachment( $file_to_attach , 'NameOfFile.pdf' );

return $email->Send();

只有一行$email-> addatattachment ();——再简单不过了。

如果使用PHP的mail()函数，则需要编写大量代码，并且可能会遇到许多很难找到的错误。

在与格式糟糕的附件斗争了一段时间后，我使用了以下代码:

$email = new PHPMailer();
$email->From      = 'from@somedomain.com';
$email->FromName  = 'FromName';
$email->Subject   = 'Subject';
$email->Body      = 'Body';
$email->AddAddress( 'to@somedomain.com' );
$email->AddAttachment( "/path/to/filename.ext" , "filename.ext", 'base64', 'application/octet-stream' );
$email->Send();

针对PHP 5.5.27的安全更新

$file = $path.$filename;
$content = file_get_contents( $file);
$content = chunk_split(base64_encode($content));
$uid = md5(uniqid(time()));
$file_name = basename($file);

// header
$header = "From: ".$from_name." <".$from_mail.">\r\n";
$header .= "Reply-To: ".$replyto."\r\n";
$header .= "MIME-Version: 1.0\r\n";
$header .= "Content-Type: multipart/mixed; boundary=\"".$uid."\"\r\n\r\n";

// message & attachment
$nmessage = "--".$uid."\r\n";
$nmessage .= "Content-type:text/plain; charset=iso-8859-1\r\n";
$nmessage .= "Content-Transfer-Encoding: 7bit\r\n\r\n";
$nmessage .= $message."\r\n\r\n";
$nmessage .= "--".$uid."\r\n";
$nmessage .= "Content-Type: application/octet-stream; name=\"".$filename."\"\r\n";
$nmessage .= "Content-Transfer-Encoding: base64\r\n";
$nmessage .= "Content-Disposition: attachment; filename=\"".$file_name."\"\r\n\r\n";
$nmessage .= $content."\r\n\r\n";
$nmessage .= "--".$uid."--";

if (mail($mailto, $subject, $nmessage, $header)) {
    return true; // Or do something here
} else {
  return false;
}