1. Go to Communications > eMail
  2. Hover over the mailing name and click Manage
  3. Next to the appropriate email, click the blue Receivers button
  4. Expand Communities
  5. Expand Forms
  6. Click Choose Event next to the appropriate Form type
  7. Select the form by selecting the appropriate radio button
  8. Choose the filter you wish (Registrants, Additional Contacts, etc)
  9. Click it to highlight, and click Add
  10. Set any additional filters in the pop-up window.
  11. Click OK
  12. Click Save and Done