⭐ Merited by ChuckBuck (1)
And you didn't provide a list of people who emailed you, how do they know if they're one of the first 16 
Well, if they see the sha256 hash of their giveaway code in the list, they'll know they were one of the first 16. How do they know who are the winner if they don't know what their sha256 hash is 
They have the giveaway code, if they create a sha256 hash of the code they have at hand, they know their slot number, so they'll know if they won. On linux, it's basically:
Code:
echo -n giveawaycode | sha256sum
On windows i have no idear, but you can use one of the many online tools to calculate a sha256 hash, like https://emn178.github.io/online-tools/sha256.html