Mailer class error

I created a helper method in a file called mailer_helper.rb that I
want to use in my mailer class. I included the helper using this
helper :mailer
even after including this I get this error:
undefined local variable or method `get_host' for #<Mailer:0x38aca0c>
any ideas?

class Mailer < ActionMailer::Base

  helper :mailer

  def contact_us(contact_us)
    @subject = 'Nu+riSum contact request'
    @recipients = ''
    @from =
    @sent_on =
    @layout = :mailer
    @body =
      :fn => contact_us.first_name,
      :ln => contact_us.last_name,
      :em =>,
      :org => contact_us.organization,
      :ph =>,
      :msg => contact_us.comments,
      :host => get_host