Effective September 30, 2023, Airbnb no longer share the guest masked email address.

https://www.airbnb.com/resources/hosting-homes/a/an-update-for-hosts-who-use-the-email-alias-feature-195

As a workaround, you can create an auto message in your PMS and put the pre-check-in template variable in the message.

Also, there are 5 ways to share the pre-check-in link with the guest.