It’s a fact now that the U.S. Postal Service recognizes Sandy Springs as the correct city address for zip codes 30328, 30350 and 30342. If you live in those zip codes, there is absolutely no confusion: the correct return address for you to use is definitely “Sandy Springs.” If you happen to live in 30327 or 30319 you can still use Sandy Springs as your city address, but it would be wise to use your zip+4 code as well. The Postal Service really only cares about correct zip codes.
I don’t recommend it, but you could probably put your return address as “Timbuctoo” and you would get your mail correctly if you have the zip+4 code included.
City of Sandy Springs Zip Code map