All Brightboxes have access to the Brightbox smtp relay:
smtp-relay.brightbox.net
You can configure the Rails ActionMailer to use the smtp relay by dropping the following lines into your production environment config (config/environments/production.rb)
ActionMailer::Base.smtp_settings = { :address => "smtp-relay.brightbox.net", :port => 25, :domain => "brightbox.net" }
The Brightbox mail relay is fine for quick low volume use, but if you're going to be sending a lot of mails on a regular basis then it's a good idea to run your own mail queue on your Brightbox (or on a dedicated Brightbox for very high volume).
This also gets you logs of your smtp transactions so you can track what is going on. It's also useful if you'd like emails from non-rails app (such as the cron daemon)
Just install the Postfix package and the default configs are a good start:
sudo apt-get install postfix
You can then use the Rails :sendmail delivery method:
ActionMailer::Base.delivery_method = :sendmail
You may need to get a reverse dns entry set up for other servers to reliably accept your mail. File a support request with the desired fqdn and we'll set this up for you.
If you are going to sending a large volume of mail then you'll want to look into tweaking the Postfix configs for this type of work.