Content-Transfer-Encoding: base64
Content-Disposition: attachment
+{$this->attachments[0]['file']}
+
+--mixed-$random_hash
+Content-Type: {$this->attachments[0]['mimetype']}; name=\"{$this->attachments[0]['name']}\"
+Content-Transfer-Encoding: base64
+Content-Disposition: attachment
+
{$this->attachments[0]['file']}
--mixed-$random_hash--
";
+
$parts[2] = $str;
// --mixed-{t.random_hash}
//Content-Type: multipart/alternative; boundary=alt-{t.random_hash}