Missing host to link to! Please provide the :host parameter, for Rails 4

You have updated the default url options for action mailer. URL helpers will take the option from action_controller settings.

config.action_controller.default_url_options = .....

BR

You should write in the following way

For Development(development.rb)

config.action_mailer.default_url_options = { :host => "localhost:3000" }

In production (production.rb)

 config.action_mailer.default_url_options = { :host => "myproductionsite.com" }

I had a similar error. The problem is in your configuration.

Try rewriting your configuration for your development.rb and test.rb like this:

config.action_mailer.default_url_options = { host: "localhost", port: 3000 }

Also check that your configuration in production.rb is written correctly like this:

config.action_mailer.default_url_options = { host: 'myherokuapp.herokuapp.com' }

For Rails 5, use:

Rails.application.routes.default_url_options[:host] = "XXX"

You can put this in a config/environments/ file (or any other initializer), or e.g. at the beginning of config/routes.rb.