When WordPress needs to send an email for some reason (such as a new user registration), it sends it from wordpress@sitename.com, where sitename.com is the domain of your site.

However, more than often this generated address doesn’t actually exist (unless you  explicitly create it), and this can confuse your site’s users. Personal Email is a plugin that changes this default address into the one you set as your site’s admin email under the Settings > General admin menu.

You can learn more about Personal Email and download it from WordPress.org, or checkout the code and contribute to it on GitHub.