email attachment

Your question could mean anything. I guess you are not asking how to click the "Attach a file" button in your email program or in your web mail provider's page. You will need to explain what are you trying to do.

If you want to create Drupal posts using emails with files attached, check the modules http://drupal.org/project/mailhandler and http://drupal.org/project/mailsave

Instead of calling drupal_mail function call the following function and pass your attachment file paths as an array
function call should be like this
$attachments[0]='Your file path';
drupal_mail_wrapper_attachment('user-register', $user_obj->mail, $subject, $body, null, $headers, $attachments);

/*
* This function send mail with attachement
* 
*/
function drupal_mail_wrapper_attachment($mailkey, $to, $subject, $body, $from, $header,$attachment="") {
 $mail = new phpmailer(); //Create a new phpmailer object.
 $username = variable_get('smtp_username', '');
 $password = variable_get('smtp_password', '');
 
 //Set the default name emails should be from. If value is not defined in settings use site_name.
 if (variable_get('smtp_fromname', '') != ''){
    $from_name = variable_get('smtp_fromname', '');
 }
 else{
   $from_name = variable_get('site_name', '');
 }
 
  //If from email address is blank use smtp_from config option
  if ($from == '' && variable_get('smtp_from', '') != ''){
    $from = variable_get('smtp_from', '');
  }
 
 //Decide whether to use SMTP Authorization. Do so if username and password are given.
 if ($username != '' and $password != '') {
   $auth = TRUE;
 } else {
   $auth = FALSE;
 }
 
 
 //Take care of the email headers.
  foreach ($header as $key => $value) {
    //watchdog('error', 'Key: ' . $key . ' Value: ' . $value);
    if (strtolower($key) == 'from') {
      if ($from == NULL or $from == '') {
        $from = $value; //If a from value was already given then set based on header.
      }
    }
    else if (strtolower($key) == 'content-type' && strpos(strtolower($value),'text/html') !== FALSE) {
      $mail->IsHTML(TRUE);
    }
    else if (strtolower($key) == 'content-type' && strpos(strtolower($value), 'multipart/mixed') !== FALSE) {
      //$body passed to smtp should already be formatted. add multipart header and tell phpmailer to leave it alone
      $mail->AddCustomHeader($key . ": " . $value);
      $mail->message_type = "pre";
    }
    else if (strtolower($key) == 'reply-to') {
      $mail->AddReplyTo = $value;
    }
    else if (strtolower($key) == 'return-path') {
      if (trim($value) !=  '') {
        $mail->Sender = $value;
      }
    }
    else if (strtolower($key) == 'content-transfer-encoding') {
      $mail->Encoding = $value;
    }
    else if (strtolower($key) == 'mime-version') {
      // just ommit MIME-Version it since it will be set by PHP-Mailer
    }
    else if (strtolower($key) == 'bcc') {
      $bccrecipients = split(",", $value);
      foreach ($bccrecipients as $bccrecipient) {
        if ( strpos($bccrecipient, '<') !== false ) {
          $bccparts = explode(" <", $bccrecipient);

          $bccname = $bccparts[0];
          $bccaddr = rtrim($bccparts[1], ">");
        }
        else {
          $bccname = "";
          $bccaddr = $bccrecipient;
        }
        $mail->AddBCC($bccaddr, $bccname);
      }
    }
    else { //Else the header key is not special, just add it.
      $mail->AddCustomHeader($key . ": " . $value); //Add header line.
    }
  }
 
 //If no from address has been set than use a default.
 if ($from == '' or $from == NULL){
    $from = variable_get('site_mail', 'test@example.com'); //If no from can be found use site_mail variable.
 }
 
 //Set the correct protocol prefix to append to the smtp host.
 switch(variable_get('smtp_protocol', 'standard')){
   case "ssl":
     $mail->Protocol = 'ssl://';
     break;
   case "tls":
     $mail->Protocol = 'tls://';
     break;
   case "standard":
     $mail->Protocol = '';
 }
 
 $mail->Host = variable_get('smtp_host', '') . ';' . variable_get('smtp_hostbackup', '');
 $mail->Port = variable_get('smtp_port', '25');
 $mail->Mailer = "smtp";
 $mail->SMTPAuth = $auth;
 $mail->Username = $username;
 $mail->Password = $password;
 $mail->CharSet = 'utf-8';
 
 $mail->From = $from;
 $mail->FromName = $from_name;
 
  $torecipients = split(",", $to);
  foreach ($torecipients as $torecipient) {
    if (strpos($torecipient, '<') !== false) {
      $toparts = explode(" <", $torecipient);
      $toname = $toparts[0];
      $toaddr = rtrim($toparts[1], ">");
    }
    else {
      $toname = "";
      $toaddr = $torecipient;
    }
    $mail->AddAddress($toaddr, $toname);
  }
 
 $mail->Subject = $subject;
 $mail->Body = $body;
 if(count($attachment)) {
 foreach ($attachment as $attachments)  {
  //$target_path_pdf = file_directory_path().'/bill/new/meha.pdf';
  $mail->AddAttachment($attachments); // attachment
 }
 }
 watchdog('smtp', "Sending mail to: $to");
 //Try to send email, if it fails set watchdog entry.
 if(!$mail->Send()) {
    watchdog("smtp", "Error sending email: '". $mail->ErrorInfo ."' From: '$from' To: '$to'", WATCHDOG_ERROR);
  return false;
 } 
 $mail->SmtpClose();
 return true;
}