We have the ability to adjust how we handle duplicates when an individual constituent record is pulling in, and when the individual is pulling into the mailing as a primary contact for an organization. We can configure if we would like to mail to the contact only, mail to the individual only or mail to the contact and individual separately in the address processing options of the invitation. 
  1. From the event record, navigate to the Invitations Tab
  2. Select the arrows to the left of the invitation, Select Edit
  3. On the Processing Options Tab, Select the Pencil next to the Address processing option have chosen for your letter:
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  1. In the Edit Address Processing Options Screen, Navigate to the Organizations Tab
  2. Edit the settings for 'If contact is also an individual' to mail either Contact Only or Individual only to remove duplicates
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  1. Save