This is a legit email :)
You can find more information about this program in our FAQ: https://epicgames.helpshift.com/a/fortnite/?s=battle-royale&f=what-is-the-fortnite-expert-beta-program-and-why-did-i-receive-an-email-to-join&p=all
This thread was added on April 30, 2019, with posts from Kimmundi.
Original Post
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