Email post author

I'm sorry for being such a spaz, I know this question has come up a number of times but I just can't figure out what I am doing wrong.

I followed the steps in this tutorial; http://www.gravityhelp.com/documentation/page/Dynamically_Populating_the_Post_Author, pasting this code into my functions.php

add_filter('gform_field_value_author_email', 'populate_post_author_email');
function populate_post_author_email($value){
    global $post;

    $author_email = get_the_author_meta('email', $post->post_author);

    return $author_email;
}

I then created a form with an email field. Selected "Allow field to be populated dynamically", then put in this value: populate_post_author_email

In the notifications section, under "Notification to User" I selected the email field in the "Send To Field"

When I tested the form I noticed two things. First, the field I tried to dynamically populate was empty, second, only admin got notification of the email.

Any help would be appreciated.
Thanks.

Website - http://www.teachmemusic.com.au
Example form - http://www.teachmemusic.com.au/listings/test-search-2/