How can I check if the user's input is in a list of values that I have?

I am trying to create an RSVP form, I have pre-defined list of email ids, I want to see if the user entered input is in the list. Based on that I want to control the form either to proceed further parts of the form or skip all the way to the end. 

Something like a white list validation. 

You can create a condition that checks if email is on the list of comma separated values: 

The condition can show or hide fields if it is not met: How-to-Show-or-Hide-Fields-Base-on-User-s-Answer