This email source does not facilitate authentication using their customers' domains. To prevent delivery failures, they modify the sending address for domains that enforce DMARC policies. As such, this reported traffic will disappear as you move a domain to p=quarantine or p=reject. https://support.betterimpact.com/volunteerimpacthelp/en/help-articles/can-better-impact-add-dkim-spf-records-for-my-organizations-email/