Time Warner Cable (aka Spectrum, Charter.net), among other companies, utilize Cloudmark for anti-SPAM services.  Cloudmark uses unique criteria including but not limited to crowd-sourcing and the number of sends to invalid email addresses when adjusting SPAM filter algorithms. Blackbaud works with Cloudmark and Time Warner Cable to remove the SPAM listing if it occurs, but it can be triggered again by subsequent attempts to invalid email addresses. This bounce message can best be avoided by verifying email addresses are valid prior to sending and that appropriate content targeting is done to ensure email isn't marked as SPAM by the recipients.