Better Word for a "Delivery Guy"
Solution 1:
For the general case, deliveryperson may sound less informal and more respectful. For the specific case of a messenger or parcel service, you can use courier.
Solution 2:
For UPS, FedEx, etc., we say "UPS driver", "FedEx driver", etc. since "driver" is gender-neutral. For pizza, we say "pizza delivery guy" because that's what we've always called that person.