Some shipping method doesn't ship to PO Box. with this extension you can easily remove those shipping method from checkout if shipping address has PO Box address or PMB address in it.
YOu can select which shipping method to be enabled if address has PO Box address or PMB address in it. If no shipping method selected it will show none. that way you can also block shipping totally
You can select for which country the validation will works. that way you can enable / disable extension functionality for desired countries
You can set an message to show when address has Po Box or PMB Box. so customers will know that why certain shipping method are not available for them.
Our extension fully compatible with One page checkout. It followed magento coding standard and it support Magento's multiple store.