task.cs

/* So I didn't really address the naming piece, but I'd start by going down this route */

public class Task : ActiveRecord
{
  public string Name { get; set; }
  public int AssignedTo_UserId { get; set; }
  public DateTime DueOn { get; set; }

  private INotifier _notifier;
  
  public Task(INotifier notifier) : this()
  {
    _notifier = notifier;
  }

  public Task()
  {
    // I feel like i'd just pass in the date in the constructor.
    // If not required I'd make DueOn nullable 
    DueOn = DateTime.Now.AddDays(1);
  }

  override void AfterInsert()
  {
    if (_notifier != null)
      _notifier.Notify(AssignedTo_UserId);
  }
}

public class EmailNotifier : INotifier {
  public void Notify(int who) {
    Email.Send(who, "New Task", "You have been assigned a new task");
  }
}

// Not sure I like the coupling of user id to notification 
// but I'll save that for a later refactor
public interface INotifier {
  void Notify(int who);
}

How would you suppress the email notification in a case where you're creating a new task, but you don't want a notification?