I don’t know how many other people who’ve upgraded to WordPress 2.3.1 are having this problem, but I’d noticed that none of my email comment notifications were coming in anymhttp://shamuswrites.com/wp-admin/post-new.php
Writeore. I sent a note about it to the wp-testers list, and found that the fix is pretty easy.
Go to wp-includes/pluggable.php and find and remove line 228:
$phpmailer->Sender = apply_filters( ‘wp_mail_from’, $from_email );
Save and re-upload the file, and you should be back in business. I’ve submitted a new ticket for the issue, so hopefully the problem will be fixed in the next revision.