Seems to be fixed now. Thanks.
see this bug trac ticket for a clean resolution.
Is it possible that the culprit is this line:
$phpmailer->Sender = apply_filters( 'wp_mail_from', $from_email );
in pluggable.php that wasn’t there in 2.3? I think it may have changed how the intermediate mail servers perceived the messages…
I am having/have had this problem, too, since 2.3.1. What changed and why did it break the “Options” setting?
