I recently upgraded from 4.7.18 to 4.7.19 (under Drupal 7.54) and now CiviSMTP (as well as my browser) gets Drupal's "Page not found" page when trying to get to my soap.php file.
Page not found
The requested page "/sites/all/modules/civicrm/extern/soap.php" could not be found.
I've confirmed the file is in place, I'm using the default Drupal .htaccess file, file permissions seem to be at their defaults (AFAIK), and I'm out of ideas. My cron jobs are also not running, but I figure there's a common cause.