Set from e-mail address for new user registration only? In Drupal 7, it's quite easy to change the body of the emails here:

/admin/config/people/accounts


However, it has no place to set the "from" email address. I'm getting lots of spam signups and want the from email address to be "noreply@mysite.com", so as to make any responses get disgarded.

Any idea how to do this? Or even what email address is set for these emails?
You can use hook_mail_alter() to change the "from" email address of any email sent out from your site. Your code would look something like...

function yourmodule_mail_alter(&amp;$message) {
  $message['from'] = $message['headers']['From'] = '"Full Name" &lt;noreply@mysite.com&gt;';
}


Also, keep in mind that just setting the "from" address may not have the desired results in all email clients (see the discussion on the Drupal issue queue). You might also need to set "sender", "errors-to" and "reply-to" based on your requirements. Those values are in the "header" of the $message variable from the code sample above.