If I'm not mistaken, I believe the information provided, in your plug-in, at:
SendPress > Settings > Information
about the CAN-SPAM Act of 2003 is inaccurate. You say:
a physical business address (no PO Box either)
However, even in the link you provide: The CAN-SPAM Act: A Compliance Guide for Business, Article 4 says:
Tell recipients where you’re located. Your message must include your valid physical postal address. This can be your current street address, a post office box you’ve registered with the U.S. Postal Service, or a private mailbox you’ve registered with a commercial mail receiving agency established under Postal Service regulations.
Pay special attention to the part in italics, above.