You can ask players to share their emails during your live event, and then export them as a csv after your event is finished.
☝️ Exporting emails after the fact is a premium feature
Step 1 - Set up your deck to ask for emails
In your deck, add a "Text Answer" slide
Enter "Please enter your email address" (or whatever instructions you like) in the middle of the slide
On the left menu click the "medal" icon with a blue dot. Toggle off "score this slide" so the blue dot disappears
On the top menu, click on the eyeballs next to the "responses" step, and the "correct" step, so both of these are crossed off (this will hide these step from the live event)
Your slide should look like the screenshot below:
Step 2 - Set up your event
When you are ready to launch your real, big live event, select "Start Event" in the top right.
In the event settings popup, check "Disable event recap for players".
(This will turn off the popup in the beginning that asks them if they want the event recap, and if so, to enter their email. This is simply to prevent you from asking for emails twice).
Be sure to check this box when you launch your real event! (Pro tip, events stay live for up to 12 hours or as long as responses are being sent, so you can launch the event in advance).
Final suggested step — test it out!
Once you've added this, try out launching an event and join in yourself. Play through like you would if you were participating during your event. This will help you understand exactly how everything will look live!
You can launch and join as many events as you like, the free account has unlimited events for up to 10 players (even on a one-time pass).
How to get email addresses after the event
Export your event as a CSV after the fact and you will have access to all the email addresses, sorted by username.