InboxLooter helps you to put certain items out of your mailbox into your inventory. The addon creates a small frame to the right of your mailbox, where you can specify the item and the minimal amount you want to take off. There's also a button to quickly get the whole money out of all mails.
It's not possible to split up stacks in your incoming mail, so the mod will try to loot the exact amount specified or - if that's not possible - loot the smallest amount bigger than the amount specified.
It doesn't work with items with c.o.d. for I don't want to be the reason you loose your whole money by mistake ;-)
InboxLooter is written in English but should work with every client.