Email headers

We generally leave any header that you add to your message intact in the outbound message. We do, however, remove any Contactlab-specific header that matches the X-Clab-(.*) expression. As a result, you should ensure that you never create custom headers for your own use with a key that matches this expression.

The following headers are always added by Contactlab:

  • List-Unsubscribe
  • List-Id
  • X-Abuse
  • X-Mailer
  • X-Clab-Family
  • X-Binding
  • DKIM-signature


Emails sent to recipients have two additional headers:

  • A Feedback-ID header
  • A second DKIM-signature using

    This is needed to enable the Gmail aggregated feedback loop.