I've been talking with a friend of mine in regards to this script and we've come across a few problems that may occur.
We've established that no upgraded, carded, or character named <item> items can't be sent since you have to know the item # (and to my knowledge those items don't get a new item #).
Also, he's having some problems with the zeny amount required, even though he has the amount required it won't let him send anything
;; but we'll look a bit more into it o.o;
:edit: Also, you can have a total of 50 messages at one time and the system is time set so it deletes all mail on monday at midnight.