code: function addAttachmentFromFile($filename, $mimetype, $attachmentFileName = null) {
          $handle = fopen($filename, "rb");
          if (FALSE === $filename) {
              throw new MaileonAPIException("Cannot read file " . $filename . ".");
          }
          $contents = '';
          while (!feof($handle)) {
              $contents .= fread($handle, 8192);
          }
          fclose($handle);
          if ($attachmentFileName === null) {
              $attachmentFileName = basename($filename);
          }
          $attachment = new Attachment($attachmentFileName, $mimetype, base64_encode($contents));
          $this->attachments[] = $attachment;
      }
docs: Read a binary file from the file system and adds it as an attachment to this transaction.
  @param $filename the file system path to read the attachment from
  @param $mimetype the mime type of the attachment
  @param null $attachmentFileName the file name to use when sending the attachment as an e-mail. If this is null,
  the basename of $filename is used instead.