main.rb

post '/contact' do
  subject = params[:title]
  body = erb :email, :layout => false

  begin
    transport = Mailer::PostmarkTransport.new(POSTMARK_API_KEY)
    transport.send_message(SENDER, RECIPIENT, subject, body) do |message|
      message.tag = "contact-form"
    end
  rescue ArgumentError
    redirect '/contact'
  end

  redirect '/contact_successful'
end