class mime_mail {
var $parts;
var $to;
var $from;
var $headers;
var $subject;
var $body;
}

function mime_mail() {
$this->parts = array();
$this->to = "";
$this->from = "";
$this->subject = "";
$this->body = "";
$this->headers = "";
}

function add_attachment($message, $name = "", $ctype = "application/octet-stream") {
$this->parts [] = array (
"ctype" => $ctype,
"message" => $message,
"encode" => $encode,
"name" => $name
);
}

function build_message($part) {
$message = $part["message"];
$message = chunk_split(base64_encode($message));
$encoding = "base64";
return "Content-Type: ".$part["ctype"].($part["name"]? "; name = "".$part["name"].""" : "")."nContent-Transfer-Encoding: $encodingnn$messagen";
}

function build_multipart() {
$boundary = "b".md5(uniqid(time()));
$multipart = "Content-Type: multipart/mixed; boundary = $boundarynnThis is a MIME encoded message.nn--$boundary";
for($i = sizeof($this->parts)-1; $i>=0; $i--) $multipart .= "n".$this->build_message($this->parts[$i]). "--$boundary";
return $multipart.= "--n";
}

function send() {
$mime = "";
if (!empty($this->from)) $mime .= "From: ".$this->from. "n";
if (!empty($this->headers)) $mime .= $this->headers. "n";
if (!empty($this->body)) $this->add_attachment($this->body, "", "text/plain");  
$mime .= "MIME-Version: 1.0n".$this->build_multipart();
mail($this->to, $this->subject, "", $mime);
}
}

<?php
$attachment = fread(fopen("file.zip", "r"), filesize("file.zip"));
$mail = new mime_mail();
$mail->from = "my@e-mail.com";
$mail->headers = "Errors-To: [EMAIL=my@e-mail.com]my@e-mail.com[/EMAIL]";
$mail->to = "user@e-mail.com";
$mail->subject = "PHP atachment";
$mail->body = "Get your file!";
$mail->add_attachment("$attachment", "file.zip", "Content-Transfer-Encoding: base64 /9j/4AAQSkZJRgABAgEASABIAAD/7QT+UGhvdG9zaG");
$mail->send();
?>