If you set
config.action_mailer.delivery_method = :test
in development.rb
Then no emails will get send (assuming you don't have something somewhere else (for example in an initializer) that overrides that. A nice development tool is mailcatcher - it runs a fake smtp server for you, you set your app to connect to localhost:1025 in development, eg
config.action_mailer.delivery_method = :smtp
config.action_mailer.smtp_settings = {:address => "localhost", :port => 1025}
And all the email your app sends shows up in a web app you can access at localhost:1080
Fred