Sending mailings to alt email addresses on contact records

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We're looking to send a mailing that needs to go to both the primary and alt email addresses listed on a contact record. Is anyone aware of a way to accomplish this? I know incident communication can be sent to both but Outreach doesn’t have a config setting for this. I believe the only time an email is automatically sent to an alt address via a mailing is if the primary address is invalid.

Thanks.