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There are following below steps need to follow.
[1] Go STORES > Configuration, redirects Configuration section.
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[2] Left panel, choose CUSTOMERS > Customer Configuration.
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[3] Right panel, Expand the Create New Account Options section.
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[4] Go To Require Emails Confirmation Section, By Default No selected.
Once clicked on drop down, There are two options as Yes & No
select Yes for email confirmation
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[5] Finally click on Save Config Button & Require Emails Confirmation set as Yes.
Once user fill frontend user registration form, Confirmation Email send to user’s email