Instead of PO BOX 1234, Anytown, ST USA you use Street Address of Post Office, Unit # PO BOX Number, Anytown ST USA.
In addition to giving you a "real" street address, it works for any services unable to otherwise deliver to a PO BOX like UPS, Fedex or DHL, because as long as they deliver during business hours, the post office will sign for your package.
I use this to great effect as package theft is so rampant in my area. It does add a one day delay since the package is signed for by my post office and not delivered into my po box until the next day. And I've had to call and complain to Amazon a few times until they stopped trying to use their vans to deliver to that address. The drivers rarely read the instructions that say "You must deliver during business hours as this is a post office." When Amazon actually ships via USPS to my po box I get the packages same day as delivery so it's the best of all scenarios. Really I don't know why people have a such hate on for the post office. I love it.
https://postalpro.usps.com/mailing/competitivepoboxes
But yeah most likely a process server will leave the post office frustrated. I'm not sure if that's a bug or a feature. :-)