Swift Mailer settings for Acquia Cloud

NOTE: The Swift Mailer Drupal module is insecure, and has been marked as unsupported. Please seek alternatives (read more) 

Symfony Mailer and Symfony Mailer Lite (which is a drop-in replacement for Swift Mailer) have specific installation instructions on the Acquia Platform.

Issue

When using the Swift Mailer Drupal module (https://www.drupal.org/project/swiftmailer) for both Acquia Cloud Classic and Acquia Cloud Platform, emails might not be sent.

Error message:

Expected response code 220 but got code "", with message "unknown shorthand flag: 'b' in -bs

Resolution

Configure Swift Mailer module in the Drupal admin user interface so that it uses the sendmail transport, using the t mode. Here is an example screenshot: