For a mail server on Linux, one of the more popular ones is using the combination of Postfix and Dovecot. They provide both the incoming and outgoing mail services. And you can also set up a web mail interface for mail users. However sometimes all you need is a simple mail server that provides just the outgoing mail services. For example, mail sent out by your Rails app using ActionMailer. Even though Dove and Postfix will no doubt more than meet your need in this situation, a lightweight Mail server called Exim would be more suitable. It is easy to set up and meets the simple need of providing an outgoing mail service.

In Rails, the default mailer is the sendmail. The setting in the environment is set up that way and looks like this:

#config/environment/production.rb
 config.action_mailer.delivery_method = :sendmail
# Defaults to:
# config.action_mailer.sendmail_settings = {
#   :location => ‘/usr/sbin/sendmail’,
#   :arguments => ‘-i -t’
# }

To use Exim with Rails, it just requires a simple change in this default setting, as it behaves much like sendmail. It will look like this:

config.action_mailer.delivery_method = :sendmailconfig.action_mailer.sendmail_settings = {
  :location => ‘/usr/sbin/sendmail’,
  :arguments => ‘-i’
}

The difference is the “-t” option. Due to the fact that Exim has a different usage for the -t option, having that option as part of the sendmail default will cause Exim to fail in sending out email. The mail sent out via ActionMailer will never get sent. So to override the default setting, merely uncomment the default setting and remove the -t option.

I learned this from personal experience where I had to scratch my head to figure out why in spite of setting up everything correctly, I still did not receive the mail sent by the ActoinMailer.

For more Exim information, go to Exim