Gmail API file attachments not shown on receiver side - php

Question

I have some Gmail API PHP code which sends an email with attachments. Attachments dispatch on sender side perfectly, even they are available in sender's sent items. But they did not show on receiver end. what could be the problem? my code looks like following.
$to = $_POST['replyTo'];
$message = $_POST['replyMsg'];
$thread_id = $_POST['thread_id'];
$subject = $_POST['MsgSubject'];
$cc = $_POST['cc'];
$bcc = $_POST['bcc'];
$strCCName = '';
$strBCCName = '';
if (!empty($cc)) {
$encodedCC = "";
if (strpos($cc, ",") !== false) {
$list = explode(",", $cc);
foreach ($list as $ccmail) {
$encodedCC .= encodeRecipients($strCCName . " <" . $ccmail . ">") . ",";
}
} else {
$encodedCC = encodeRecipients($strCCName . " <" . $cc . ">");
}
}
if (!empty($bcc)) {
$encodedBCC = "";
if (strpos($bcc, ",") !== false) {
$list = explode(",", $bcc);
foreach ($list as $bccmail) {
$encodedBCC .= encodeRecipients($strCCName . " <" . $bccmail . ">") . ",";
}
} else {
$encodedCC = encodeRecipients($strCCName . " <" . $bcc . ">");
}
}
$strMailContent = $message;
$strMailTextVersion = strip_tags($strMailContent, '');
$strRawMessage = "";
$boundary = uniqid(rand(), true);
$subjectCharset = $charset = 'utf-8';
$strToMailName = '';
$strToMail = $to;
$strSesFromName = $_SESSION['userData']['first_name']." ".$_SESSION['userData']['last_name'];
$strSesFromEmail = $_SESSION['userData']['email'];
$strSubject = $subject;
$strRawMessage .= 'To: ' . encodeRecipients($strToMailName . " <" . $strToMail . ">") . "\r\n";
$strRawMessage .= 'From: '. encodeRecipients($strSesFromName . " <" . $strSesFromEmail . ">") . "\r\n";
if (!empty($cc)) {
$strRawMessage .= 'Cc: ' . $encodedCC . "\r\n";
}
if (!empty($bcc)) {
$strRawMessage .= 'Bcc: ' . $encodedBCC . "\r\n";
}
$strRawMessage .= 'Subject: =?' . $subjectCharset . '?B?' . base64_encode($strSubject) . "?=\r\n";
$strRawMessage .= 'MIME-Version: 1.0' . "\r\n";
$strRawMessage .= 'Content-type: Multipart/Alternative; boundary="' . $boundary . '"' . "\r\n";
/**** check if message contains any attachments *****/
if(count($_FILES['attachment']['name']) > 0){
//Loop through each file
for($i=0; $i<count($_FILES['attachment']['name']); $i++) {
$j=$i+1;
//Get the temp file path
$filePath = $_FILES['attachment']['tmp_name'][$i];
//Make sure we have a filepath
if($filePath != ""){
$fileName=$_FILES['attachment']['name'][$i];
$finfo = finfo_open(FILEINFO_MIME_TYPE); // return mime type ala mimetype extension
$mimeType = finfo_file($finfo, $filePath);
$fileData = base64_encode(file_get_contents($filePath));
$strRawMessage .= "\r\n--{$boundary}\r\n";
$strRawMessage .= 'Content-Type: '. $mimeType .'; name="'. $fileName .'";' . "\r\n";
$strRawMessage .= 'Content-ID: <' . $strSesFromEmail . '>' . "\r\n";
$strRawMessage .= 'Content-Description: ' . $fileName . ';' . "\r\n";
$strRawMessage .= 'Content-Disposition: attachment; filename="' . $fileName . '"; size=' . filesize($filePath). ';' . "\r\n";
$strRawMessage .= 'Content-Transfer-Encoding: base64' . "\r\n\r\n";
$strRawMessage .= chunk_split(base64_encode(file_get_contents($filePath)), 76, "\n") . "\r\n";
$strRawMessage .= '--' . $boundary . "\r\n";
}
}
}
/*****/
$strRawMessage .= "\r\n--{$boundary}\r\n";
$strRawMessage .= 'Content-Type: text/plain; charset=' . $charset . "\r\n";
$strRawMessage .= 'Content-Transfer-Encoding: 7bit' . "\r\n\r\n";
$strRawMessage .= $strMailTextVersion . "\r\n";
$strRawMessage .= "--{$boundary}\r\n";
$strRawMessage .= 'Content-Type: text/html; charset=' . $charset . "\r\n";
$strRawMessage .= 'Content-Transfer-Encoding: quoted-printable' . "\r\n\r\n";
$strRawMessage .= $strMailContent . "\r\n";
try {
// The message needs to be encoded in Base64URL
$mime = rtrim(strtr(base64_encode($strRawMessage), '+/', '-_'), '=');
$msg = new Google_Service_Gmail_Message();
$msg->setRaw($mime);
$msg->setThreadId($thread_id);
$objSentMsg = $service->users_messages->send("me", $msg);
echo "msg sent!";
} catch (Exception $e) {
print($e->getMessage());
}
its been couple of hours messing around but didn't find anything. Can anyone help me out of this? Thanks.