Currently, only a maximum of 5 tasks are shown for Due Today, Due Tomorrow and Overdue. So the email should contain at least 20 if not more tasks per group, to make sure, you see all tasks in most cases without having to click extra to get an overview.

PS: The link "+ x more" does NOT open the very same list with all entries (which would be expected). This should be improved as well, since I don't want to start searching again for the content that has already been prepared in the email.