Undefined variable $filetype. Wrong variable name used in SmtpMailSystem::mail(). Should be $file_type

This is a bug in the SMTP module.
From SmtpMailSystem::mail():

$file_path     = $this->_get_substring($body_part, 'filename=', '"', '"');
$file_name     = $this->_get_substring($body_part, ' name=', '"', '"');
$file_encoding = $this->_get_substring($body_part, 'Content-Transfer-Encoding', ' ', "\n");
$file_type     = $this->_get_substring($body_part, 'Content-Type', ' ', ';');

if (file_exists($file_path)) {
  if (!$mailer->AddAttachment($file_path, $file_name, $file_encoding, $filetype)) {
    drupal_set_message(t('Attahment could not be found or accessed.'));
  }
}

As you can see, $mailer->AddAttachment() is given a non-existing variable ($filetype) as an argument. It should be $file_type, as this variable is defined above. Moving to the SMTP module issue queue.

Here's a patch against 7.x-1.x for the committer.

Thanks, committed.