Good Natural Key For a Physical Mailing Address
As mentioned in the comments, free text fields make it tough to create a primary key on. And for something with as much variability as an address field, it's just not reasonably possible by itself.
This is the type of problem where if you must create a primary key for it, then you will need to use strong validation and/or an address standardization API like this one from the USPS, in your application layer before it hits the database. Even doing that, I don't think you'll have a 100% perfect solution, but it does make it more reasonably possible to then create a primary key on an address field.