I also think that perhaps it shouldnt charge you Mithril Coins for mailing the items to your own characters. Yes. I know this minimizes the need for Shared Storage, but I think people will still prefer shared storage. Especially as they get sick of alting around and juggling their stuff.
This is how we built the system. There are two new rules for the kinds of items you can mail that you couldn't before:
1. If you are mailing one of your alts, you can mail any bound-to-account item, whether purchased from the store or not. You will only be charged regular postage, not mithril.
2. If you are mailing someone else, you can mail a bound-to-account, purchased from the store item, for mithril coins
Let us know if something isn't working. Because the rules and amount of postage we charge now depend on the user you are sending to, there are some awkward UI cases where you are dragging items in that are valid but then become invalid because you change the user. We tried to make them all work reasonably well .