In addition to those suggestions listed (though I'm not sure charging for mail would be a hinderance to the gold sellers), perhaps having some arbitrary limit on the number of mails sent per day/week/hour would be good. I mean... who really needs to send more than a dozen or two mail messages per day, really? I'd also like…
They appear to give you items that are at the "x9" level below you. IE, open one at level 39... you get a 39 item. Open it at 41, you get a 39 item. Open it at 50, you get a 49 item. etc.