On January 3, 2019, we became aware of a problem with the integration between our donation platform, DonorBox, and MailChimp, in which all donor emails were being sent to MailChimp without filtering for opt in/out. As a result, everyone received email from us regardless of whether or not they opted in or out.
This happened because when we set up our DonorBox account, apparently a custom checkbox was used without filtering logic associated with it. The custom checkbox essentially did nothing. We should have been using the default checkbox for opt-in and opt-out.
To remediate, we unsubscribed all donors who had selected to opt out of communications from our MailChimp database. We also fixed our DonorBox account setup so that it will only push opted-in donors to our MailChimp account.