Error sending email with Mandrill

Contact.rb template:

class Contact
  include ActiveModel::Validations
  include ActiveModel::Conversion
  extend ActiveModel::Naming

  attr_accessor :name, :email, :message, :subject

  validates_presence_of :name, :subject, :email, :message
  validates_format_of :email, with: /\A[a-z0-9.]+(\+[a-z0-9_-]+)?@[a-z0-9.-]+\.[a-z]{2,4}\z/
  validates_length_of :message, minimum: 10, maximum: 500

  def initialize(attributes = {})
    attributes.each do |name, value|
      send("#{name}=", value)
    end
  end

  def persisted?
    false
 end

end

Controller:

def sendemail    
  @contact = Contact.new(set_params)
  if @contact.valid?
    PageContact.contact_message(@contact).deliver
    flash.notice = "E-mail enviado com sucesso!"
  else
    flash.alert = "* Preencha os campos corretamente."
  end          
  redirect_to root_path
end

private
  def set_params
    params.permit(:name, :email, :subject, :message)
  end

config / environments / development.rb

config.action_mailer.delivery_method = :smtp
#config.action_mailer.smtp_settings = { :address => "localhost", :port => 1025 }
config.action_mailer.smtp_settings = {
  :address              => "smtp.mandrillapp.com",
  :port                 => 587,
  :domain               => 'http://localhost:3000',
  :user_name            => ENV['EMAIL_USER'],
  :password             => ENV['EMAIL_PWD'],
  :authentication       => 'login',
  :enable_starttls_auto => true
}

app / views / home / index.html.haml

%div{:class=>"8u 12u$(small)"}
  = form_tag root_path do
    %div{:class=>"row uniform 50%"}
      %div{:class=>"12u 12u$(xsmall)"}
        = text_field_tag :name, nil, placeholder: "Nome", required: true
      %div{:class=>"12u 12u$(xsmall)"}
        = text_field_tag :subject, nil, placeholder: "Assunto", required: true
      %div{:class=>"12u$"}
        = email_field_tag :email, nil, placeholder: "E-mail", required: true
      %div{:class=>"12u$"}
        = text_area_tag :message, nil, rows: 4, placeholder: "Mensagem", required: true
    %br
    %ul.actions
      %li
        = submit_tag "Enviar"

The problem I noticed is that it is not undergoing validation.