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 statement: 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 = 'me@me.com'     @from = contact_us.email     @sent_on = Time.now     @layout = :mailer     @body =     {       :fn => contact_us.first_name,       :ln => contact_us.last_name,       :em => contact_us.email,       :org => contact_us.organization,       :ph => contact_us.phone,       :msg => contact_us.comments,       :host => get_host     }   end