2) By the user
a) The author of the blog needs to include a small text input field on the blog home page.
b) Here readers can subscribe themselves to the blog by adding their email address in the text box. The code required for this is here and may be placed in the sidebar (modify the "main entry" template to accomplish this) or other location on the blog.
This particular script returns a pop-up box when an email address is added, so that the user doesn't add himself several times.
The mt-add-notify.cgi is the script that is run in Movable Type to add the feature of email notification. Essentially this piece of code creates a form where the user can input his/her email address in the text box. On clicking the add button the mt-add-notify.cgi file is invoked, which will in turn add the user to the notification list.