Pings on membership

Hi, thanks to these threads pings on membership was much easier than I thought to set up.
https://premium.wpmudev.org/forums/topic/about-pings-in-membership-plugin-exactly-which-are-the-keys-here
https://premium.wpmudev.org/wp-content/uploads/2012/03/Membership-Docs-3027.pdf
https://premium.wpmudev.org/forums/topic/pings-on-membership

2 Questions:
1. The email seems to be coming from some email address that I am not familiar with on my server www-data <www-data@mydomain-1.myservercompany.com> I want to change the from address to one that I want.
I tried essentialtalks's suggestion in this post of adding
$headers .= 'From: ' . $_POST['username'] . ' <' . $_POST['email'] . '>';
to pingtest.php but it didn't work.

I then tried Barry's suggestion of adding
mail($to, $subject, $message, $headers, "-f $_POST['email']");
to pingtest.php but that didn't work either.

2. I saw in the notes that I can just change the pingtest.php field
$to = 'my@email.com';
to my email address and it worked, what do I enter so that the subsite admin or subscriber gets the message, so that I don't have to manually enter the email address each time?