Добавьте файлы проекта.

Models/Contact.cs

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+using System.ComponentModel.DataAnnotations;
+using System.Net.Mail;
+
+namespace ContactsApp
+{
+    public class Contact
+    {
+        public Guid Id { get; }
+        public string Name { get; set; }
+        public string? Email { get; set; }
+        public string Phone { get; set; }
+
+        public Contact(string name, string? email, string phone)
+        {
+            Id = Guid.NewGuid();
+            Name = name;
+            
+            try
+            {
+                var addr = new MailAddress(email);
+                Email = email;
+            }
+            catch (Exception ex)
+            {
+                throw new Exception("Invalid email");
+            }
+
+            Phone = phone;
+        }
+    }
+}
+
+