Per the CAN-SPAM Act your organization can no longer contact those addresses and Blackbaud is not allowed to give that information out as this would be considered  illegal and could result in fines to the Organization and Blackbaud if reported.

Please review The Federal Trade Commission CAN-SPAM Act: Compliance Guide for details.

The way it works:

A recipient no longer wishes to receive email from an organization; They click 'THIS IS SPAM' or your organization's email system identifies the mailing as spam based on settings put in place by your email administrator for filtering email.  

We receive that notice and must, within ten days, suppress further sends from your site to that user.

If, at a later time, the user wants to start receiving emails again they must contact your organization, you should not pro-actively reach out to them.  

Advise the user that to be removed from the blacklist they must send an email from the email address in question, so we know it is a valid request, to and we will take them off the Blacklist.

Refer to the following article for what should be included in the email: How to have an email address removed from the Blackbaud blacklist

This is purposely designed this way as the law says when a person wants out they must be allowed out and have the expectation that no further contact from the organization will occur unless the person initiates that contact.