```ruby
class ContactMailer < ApplicationMailer

  def contact_us(contact_id)
    @page_content = Page.guaranteed_find slug: 'contacts-mailer-contact-us'
    @contact = Contact.find contact_id

    mail(
      to: @contact.email,
      subject: @contact.subject
    )
  end
end
```

Add unique_args to contact_us mailer
user
```ruby
class ContactMailer < ApplicationMailer

  def contact_us(contact_id)
    @page_content = Page.guaranteed_find slug: 'contacts-mailer-contact-us'
    @contact = Contact.find contact_id
    headers( unique_args: {
        mailer: "ContactMailer"
      }
    )
    mail(
      to: @contact.email,
      subject: @contact.subject
    )
  end
end
```
assistant