It sounds like your messages fall squarely into the "transaction or relationship message" (TORM) category described in the CAN-SPAM Act, Section 3,
Definition #17. Take a look at the FTC's "
Compliance Guide for Business". The "Guide" tells you that a TORM "may not contain false or misleading routing information, but is otherwise exempt from most provisions of the CAN-SPAM Act." If you are considering solutions that cannot support a "TORM-only" message flow, keep looking.