I have installed amavis-new on my mail system to block incoming mails with invalid characters in header.
Each time I receive a mail from my weblog the mail gets blocked. I have found the reason.
In wp-includes/functions.php, the functions wp_notify_postauthor and wp_notify_moderator include \r (carrage return?) characters in the mail header. I think they're not allowed. A \n (new line) should be enough.
Using WordPress 1.2 on Linux, Apache, PHP 4.3.8