I can send emails with Drupal 7 using the SMTP Module but not CiviCRM
Civicrm has changed how it's including the PEAR library - it was previously including a patched version - however this was updated in https://github.com/civicrm/civicrm-core/commit/a6a0ff13d2a155ad962529595dceaef728116f96# to improve maintainability 

I believe if you want to apply the fix from SMTP connection failing problem 

you will now find the required file in vendor/pear/net_smtp/Net/SMTP.php