Redmine: The following error occured while sending email notification: 530 5.7.0 Must issue a STARTTLS command first.
Recently while working on a CentOS Linux server I downgraded Ruby version 1.8.7 p302 to Ruby version 1.8.6 p399 because of a project that was built for Ruby 1.8.6. The server is a development CentOS Linux server with numerous other projects already operational on it and so downgrading Ruby caused a couple issues one of which was with Redmine project management software. The issue was with sending email notifications for things such as file uploads, added issues, issue updates, etc. Below I describe the error in more detail, the reason for the error, and how to resolve the error sending email notifications.