public class Account
{
    [Key]
    public int Id { get; set; }

    [Index(IsUnique = true), Required]
    public string UserName { get; set; }

    [Required]
    public string Password { get; set; }

    [Required]
    public string Email { get; set; }
}

var account = new Account
{
     UserName = "X",
     Password = "X",
     Email = "NotValidEmail"
}