Code wise, it's troubling that you have 2 code paths which do more or less the same thing. Customizing the email messages that go out subsequently becomes a disjointed task.
a) ~/app_code/extenstions/SendCommentMail.cs loads from global.asax in application start (way confusing)
b) Post.SendNotifications more or less does the same thing but to a different audience of recipients.
Is there any way you can remove the
Extension in future versions and collapse these into 2 methods called from inside Post.cs: