Sorry, I completely missed that this was regarding the User Registration Add-on.
The notification you're referring to comes from WordPress, so you'd have to configure WordPress to send it differently. There are a couple plugins I know of that will allow you to change the registration email, including the "from" address. Here's one (I have not tested it):
The WP Mail SMTP plugin is designed for more reliable mail delivery from your website, but it too allows you to configure the "from" email:
Posted 11 years ago on Sunday August 21, 2011 | Permalink