ActionMailer is a very handy class for sending emails from your rails application. However, the problem that typically arises is the sending of links to your site via rails using the url_for method. Acording to the API documentation, this is because the mailer instance does not have any context about the incoming request. The API documentation recommends passing the host to the url_for parameter, like this:

url_for(:host => "www.myproductionsite.com",
        :controller => :home,
        :action => :index)

However, when using multiple url_for calls in a model, this can lead to a violation of DRY. Therefore, the typical resolution to this has been to add some declarations to your class, like this:

class Notification < ActionMailer::Base
  default_url_options[:host] = "www.myproductionsite.com"
end

I dont really care for this approach, as it locks my model into operating under the assumptions of a particular environment. I am unable to verify the links in my development or test environments without some string manipulation. A little effort led me to this approach, which so far seems to be much better. Instead of declaring the default_url_options in the ActionMailer model, I’m including them in config/environments/*.rb in this way.

# development.rb and test.rb
class ActionMailer::Base
  default_url_options[:host] = "localhost"
  default_url_options[:port] = 3000
end

# production.rb
class ActionMailer::Base
  default_url_options[:host] = "www.myproductionsite.com"
end

I am taking advantage of the environments file to give me the benefits of custom url options based on the environment that I am currently executing in. This is precisely what these files were designed for.