@Simon:This issue also occurs with Hotmail and Gmail accounts (using Exchange ActiveSync Protocol). The worst part about it is that with Gmail archiving, it continues to show the message as unread in the your account until you manually mark it read. I reported this nearly 6 months ago via @winphonesupport. I was told that they would pass it on to the Windows Phone Team. This has been an issue since the Windows Mobile days. With everyone at Microsoft presumably using Exchange for their work e-mail, I really don't understand how this bug has slipped through the cracks for so long. Regardless, I hope Mango includes a fix for it.