After I upgraded to 2.3.1 I ran into a comment e-mail notification glitch. First, when someone entered a comment, the e-mail was now sent to the e-mail account "wordpress" rather than the admin contact e-mail account I listed within WordPress. Second, it was being sent to the ISP's assigned hostname, not the actual URL of the Web site. [My ISP assigns a sub-domain type URL for accounts that are created before there's an actual Web address. In this case, gdwallen.securesites.net instead of http://www.ifoapplestore.com. Turns out I couldn't add a "wordpress" user to that Web alias. So I went into the ~/wp-includes/pluggable.php file and changed the "wordpress" reference to "root". That sent the e-mail to an account that I could access. I don't know why the e-mail address changed or why it was picking up the hostname from php internal variables. But that's the fix.