ALK removed all P.O. Box ZIP codes (U.S. and Canada) from our data in 2008 because:

• Distances using P.O. Box codes are inaccurate - often 10 or more miles shorter or longer than the miles to the ZIP code for the physical delivery location. 
• P.O. Box codes are incompatible with street addresses. This can result in manual lookup of addresses, incorrect driving directions, and costly back-tracking.
• The shippers and carriers you do business with may not accept old and obsolete ZIP codes or P.O. Box codes, which may delay payment while bills are corrected.

Tools to use to determine if a ZIP code is a P.O. Box

• In the U.S., the USPS website has a ZIP Code locator.
• Canada Post maintains a similar site.