NotificationService.cs

public class NotificationService
{
    public void NewCustomer(Customer customer)
    {
        var msg = $"You have a new customer called: {customer.Name}";

        var smpt = new SmtpClient("smtp.example.com", 25);
        
        var smtpMessage = new SmtpMessag();
        smtpMessage.Subject = "New customer";
        smtpMessage.To = "bob@example.com";
        smtpMessage.Body = msg;
        
        smpt.Send(smtpMessage);
    }
}