bbPress.org

I think in your code the function no_reply_email needs a my_bbp in front of it

so

function no_reply_email(){
    $email = 'no-reply@sitename.com'; // any email you want
    return $email;
}
add_filter('bbp_get_do_not_reply_address','my_bbp_no_reply_email');

shoudl read this

function my_bbp_no_reply_email(){
    $email = 'no-reply@sitename.com'; // any email you want
    return $email;
}
add_filter('bbp_get_do_not_reply_address','my_bbp_no_reply_email');