Rails 3 - Delayed_Job (collectiveidea), trying to Delay Mailers - Error: NoMethodError (undefined method `delay' for UserMailer:Class):

Hello, I have the following in an observer:

    UserMailer.delay.msg_notification(record)

In user_mailer.rb
class UserMailer < ActionMailer::Base
...
def msg_notification(record)
    mail(
          :to => "#{record.user.email}",
          :subject => "Notification"
          )
  end
..
end

But this errors with:

NoMethodError (undefined method `delay' for UserMailer:Class):

Any ideas? thanks