Still have not come around to installing this and configuring it for the current project.. would like to get back to this. At this stage, only preliminary research has been done for the email configuration with Rails. A longer, more in depth post will come at a later point in time.
Configure OpenSMTPD as Relay
Make sure OpenSMTPD is working with sendmail
Configure rails to properly use Sendmail
Configure Rails in a container to properly use Sendmail
Test Rails Development
Test Rails Production
Docker OpenSMTPD Container Image