Good Natural Key For a Physical Mailing Address

I'm trying to figure out what a good natural key for a Physical Mailing (PO Box) address would be. I haven't designed the fields for the table yet, and initially I was going to go with a surrogate key and a text field for the address, allowing free input. But the other dev I'm working with is interested in having a natural key (just for this one table). However, it's not quite making sense to me, because I'm not sure how to ensure, with an address, properly input data (when keyed in either on create or to do some kind of manual lookup). I know that you can often format the same address in more than one way. For example:

Suite vs Ste.
Apt. 36 vs #36 vs Unit 36
1110 West 300 South vs 1110 W 300 South vs 1110 W. 300 S. vs....

All valid, but all different. Granted PO Boxes are more standardized, but I feel like it may still suffer from some of the same issues. Any thoughts on the matter would be *greatly* appreciated!