I'm setting up a server with Ruby to deploy a Rails application. I'm planning on using Mandrill or SendGrid (i.e. providers of transactional email services) to send notification emails and that type of thing. On my local machine, I can connect to their services via environment variables that connect to their api. In that type of situation, it's unclear to me whether I need to install something like Postfix. https://www.digitalocean.com/community/articles/how-to-install-and-setup-postfix-on-ubuntu-12-04