Genshin Impact has a number of mail promotions that are good for earning free rewards and Primogems, so make sure you keep an eye out for them as they will be released very soon!
Promotion on your Character’s Birthday – Check Your Mail!
If you log in on the birthday of one of the characters, they will share a letter and some items with you!
Promotion on your (the Player’s) Birthday Promotion – Check Your Mail!
The characters are not the only ones who get to celebrate their birthdays – you do too! On the date you set as your birthday in-game, you will get a special cake that stays in your inventory even after you use it.
Promotion Rewards from Redeem Codes – Check Your Mail!
Aside from the Mail rewards listed on this page, miHoYo will also send all rewards from redeeming codes through their website to your in-game mail as well.
Promotion Rewards from Surveys – Check Your Mail!
Occasionally, Mihoyo issues some survey that players can take to recieve some Mora. While the reward isn’t the best, the player’s input in their surveys ensures us better content in the future.