MailTips shows you what is attached to a mail without having to open the message by hovering over a message in your mailbox.
When there are stacks of items attached to a mail the tooltip will only show the total of each item attached, so 2 stacks of 20 Linen Cloth will be displayed in the tooltip as 40 Linen Cloth attached to the mail.
You can also follow MailTips on Twitter. Update notifications and known issues will be posted on Twitter.