Claim type Error.Not getting the Email.Returning Null

This is my AppUser Class:

 public class AppUser
    public int Id { get; set; }

    public string email { get; set; }
    public string userFirstName { get; set; }

    public string userLastName { get; set; }


Now if I Claim User by this Commands

var userEmail =  User.FindFirstValue(ClaimTypes.Email) 
var userEmail =  User.FindFirstValue(ClaimTypes.Name)

returns No Content/Null, But if I Claim this command,

var userEmail =  User.FindFirstValue(ClaimTypes.NameIdentifier)

returns userFirstName of AppUser Class,even not the ID.

Why these is behaving like this?I am using 5.0.1.

Specially I want to get the email of the user. How can I do it ?