We've encountered a bit of confusion from some people who have pre-ordered the game, but not received the beta invitation email. Please remember that you will ONLY receive the email if you signed up for the Age of Empires Insiders Program with the same Microsoft Account email that you pre-ordered the game with.
If you do not receive the invitation email within 7-10 days of pre-ordering that is likely why. Don't worry though, you do not need the welcome email to access the beta; it just provides the instructions for how to download it, which you can now find below:
Installing the Age of Empires: Definitive Edition Beta on Your Windows 10 PC
Getting Access to the Age of Empires: Definitive Edition Beta Forum
If you pre-ordered, but have not signed up for the Age of Empires Insiders Program, you still will not have access to the hidden Closed Beta forums. If that is the case, please private message myself (@jennywaboom) or @snickerdoodle letting us know your Gamertag and MSA, and we will work on getting you access. Please be patient, as there are a lot of requests for us to get through.
If you did sign up for the Age Insiders Program, then you will be granted forum access within 7-10 days, along with the Beta invitation email. Again, please be patient, it will come! Message myself or @snickerdoodle if you haven't received access within the 7-10 day window.