Shoutbox

As soon as a mail client (WLMail) checks your mail, all the new mail is flagged as being 'notified upon'. So of course you're not going to get a new-mail notification anymore for those mails in other programs which check if new mail has arrived (eg: WLMessenger).

This sounds like an issue of WLMail though, nothing todo with Messenger (and thus should go to TechTalk)....