Hmm, I'm not sure how practical or effective that would be. I don't know how UC could check this. I've seen addresses like "PO Box", "P.O. Box", "POB", PMB", "RR Box", "Box", "#", etc. Some of these aren't actually boxes at a post office, they're boxes at a storefront like Mail Boxes Etc., or a college campus, or some such place which UPS DOES deliver to, even though the address has a box number. And sometimes people will fill in both their street address AND a PO Box number (presumably to allow me to choose based on shipping method). I don't know how you could write a regexp covering all these cases. UPS doesn't even try to do this - UPS quotes on the UPS site are not based on the street address, only the City/ZIP plus the package information.

IMO it is better to just print a disclaimer about "UPS does not ship to PO Boxes" and let the customer deal with it. If it's a frequent occurrence, throw up a modal dialog like the terms and conditions contribution to make sure they see and agree with the address restrictions before they can submit the order.

It may be a little unfriendly, but I decided long ago to just ship to the address the customer provides, even if it looks wrong. I just don't have the time or patience to go back and forth via e-mail trying to figure out what the customer "meant" to enter. They get several chances during the order process to enter their address and review the order information - if they get it wrong it's their fault. I just address the package as they entered it, and if it gets bounced back to me THEN I send them an e-mail saying they provided a wrong address and if they want their merchandise they need to pay for a second shipping. The few times it's happened I've received both the second payment and an apology from the customer, so I don't think my policy is making enemies... I've even had repeat orders (with the correct address ) from at least one of these customers.

If people are apologetic about giving the "wrong" address, that just proves that people are sheep. A seller should have no problem shipping to *any* legitimate address, particularly one as mainstream as a USPS PO box. If UPS has a problem with that, then a service such as USPS or DHL Direct should be used.

The Customer Is Always Right