When someone joins our mailing we do nothing outside of thanking them on the site following the signup.
We only contact them as part of a mass emailing with mail chimp letting them know when we have our big annual sale with the discount code to use.
In the past we would sometimes send out newsletters but that generally led to people opting out of the mailing list and didn't really lead to more views on the site, so we stopped sending those.
We've tried newsletters - People don't want to read and opt out.
We've tried videos - People don't want to click and opt out.
We've tried special discounts for those that sign up - They use it and you never see them again.
Now what HAS worked for us is....
Product testing. We're constantly looking to release new products and because of that we need extensive feedback from real customers interested in trying it. So before we even release it we have a few customers trying it. I'd say we get about 20-25 emails a day from different people that are highly interested in this opportunity (in other words, they come to us) and their feedback has changed our products to improve them and our sales.
It's a good system. That's all the goods I can give.
You might think, "isn't that what fiverr does?" Fiverr is reviews for free products. Our system is different. We haven't even released the product and have customers providing feedback through pictures, videos, suggestions, etc. Then we make the necessary changes and launch.
Reviews come later from those that actually buy the product. I wouldn't necessarily give something away. You should get something back. In our case we get good and brutal feedback that helps us make better products before we even attempt to make a sale.
I think it was Bill Gates (in the days of Microsoft) that once said something along the lines of 'I learned more from unhappy customers than happy ones'.