gistfile1.ru

def deliver_welcome!
  reset_perishable_token!
  Notifier.deliver_welcome(self)
end

#Welcome method in Notifier

def welcome(user)
  subject       "Welcome to aplication name!"
  from          "Aplication name<admin@aplication.com>"
  recipients    user.email
  sent_on       Time.now
  body          :application_url => application_root_url(:subdomain => user.company.sub_domain)
end

And I am using @application_url in mail body