It’s pretty normal to be told that a post office box, as registered at a post office in the United States, doesn’t count as a physical address. And for some things, it really doesn’t. But for CAN-SPAM and email marketing, a PO box works just fine.
The Federal Trade Commission website has a guide called “CAN-SPAM Act: A Compliance Guide for Business” that makes it clear that a PO box counts as a physical address for CAN-SPAM compliance and marketing purposes, and I’ve emphasized the relevant passage.
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.
https://www.ftc.gov/business-guidance/resources/can-spam-act-compliance-guide-business
The key language there is that your message must include your valid physical postal address. Which a PO box is.
So if you were worried you needed something other than a PO box for your email marketing to stay in compliance with U.S. spam laws, don’t be. :)
If you haven’t read the entire CAN-SPAM guide, you should take the time to read it. It’s not as dull as you’d think. :)