Please help us help you and fill where relevant:
Your LimeSurvey version: 6.5.6
Own server or LimeSurvey hosting: limequery.com hosting
Survey theme/template: Fruity
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Dear all,

Is the following design possible? Our goal is to reduce the questions an existing participant needs to answer. 

1. Load all existing users into the central participant database
2. The first question will be asking for email address
3. Following that, there will be a hidden question to find out whether a new response is from a new user or an existing user who is already in the central participant database
4. If the email already exists in the central participant database, a bunch of questions will be skipped. 

Thanks!

Not out of the box, clearly.

Something to construct via a plugin