uninitialized constant ApplicationMailer - ruby-on-rails

Question

I'm trying to make a contact form work by following this tutorial, but I keep having the error : uninitialized constant ApplicationMailer after i submit the form.
the traces give the following informations:
app/mailers/message_mailer.rb:1:in <top (required)>'
app/controllers/messages_controller.rb:9:in create'
actionpack (4.2.5) lib/action_controller/metal/implicit_render.rb:4:in send_action'
actionpack (4.2.5) lib/abstract_controller/base.rb:198:in process_action'
actionpack (4.2.5) lib/action_controller/metal/rendering.rb:10:in process_action'
actionpack (4.2.5) lib/abstract_controller/callbacks.rb:20:in block in process_action'
activesupport (4.2.5) lib/active_support/callbacks.rb:117:in call'
activesupport (4.2.5) lib/active_support/callbacks.rb:117:in call'
activesupport (4.2.5) lib/active_support/callbacks.rb:555:in block (2 levels) in compile'
activesupport (4.2.5) lib/active_support/callbacks.rb:505:in call'
activesupport (4.2.5) lib/active_support/callbacks.rb:505:in call'
activesupport (4.2.5) lib/active_support/callbacks.rb:92:in __run_callbacks__'
activesupport (4.2.5) lib/active_support/callbacks.rb:778:in _run_process_action_callbacks'`
Here are the file i have :
controllers/messages_controller.rb
class MessagesController < ApplicationController
def new
#message = Message.new
end
def create
#message = Message.new(message_params)
if #message.valid?
MessageMailer.message_me(#message).deliver_now
redirect_to new_message_path, notice: "Thankyou for your message."
else
render :new
end
end
private
def message_params
params.require(:message).permit(:name, :email, :subject, :content)
end
end
models/message.rb
class Message
include ActiveModel::Model
attr_accessor :name, :email, :subject, :content
validates :name, :email, :subject, :content, presence: true
end
mailers/message_mailer.rb
class MessageMailer < ApplicationMailer
default :to => "jd.levarato#gmail.com"
def message_me(msg)
#msg = msg
mail from: #msg.email, subject: #msg.subject, body: #msg.content
end
end

Answer 1

You have to create ApplicationMailer class that inherits from ActionMailer::Base.
application_mailer.rb
class ApplicationMailer < ActionMailer::Base
default from: 'from#exmaple.com'
layout 'mailer'
end
Or you can simply inherit ActionMailer::Base to your MessageMailer
class MessageMailer < ActionMailer::Base
default :to => "jd.levarato#gmail.com"
def message_me(msg)
#msg = msg
mail from: #msg.email, subject: #msg.subject, body: #msg.content
end
end