This plugin makes WordPress specify the sender email address correctly in outgoing emails.
WordPress by default does not send emails with a correctly specified sending email address. By default outgoing emails from a WordPress installation is sent with user id of webserver process and hostname of webserver as the email address. This isn't correct and many hosting providers block such emails, mainly because of spam.
So this plugin makes sure that a correct sender address is set, by setting the Sender property of the PHPMailer object in WordPress.