But you can get the deal even if you don't send them anything back. They say it's on the honor system, and they suggest that you might also donate some nail polish instead of disposing of it. You'll get each bottle for $4.50 with this deal.
Use code EARTHLUV from April 21-28. All the information is here.
Zoya's one of my favorite nail polish brands. Possibly my very favorite. They just make such fucking interesting shades and they have a million of them. I've been happy with almost all the ones I've bought, and I've never paid full price, because they frequently have good sales. I'm going to have to sit this one out this year, because I just can't afford any more polish, but if anyone goes for it, show me what you get!
Here's one of my favorites, Giovanna (more here):