command..

If send_mail is anything to go by, the first two parameters of send_item_mail will definitely be recipient and mail subject in that order.The problem thereafter lies in the rest of the parameters; what's still needed is 'message', 'mail type (regular or express)', 'coin (send gold? cash on delivery?)', and an item being sent as well. As previously mentioned, sending a mail with COD and no item will get the error message currently being encountered; indicating that people trying to use this command are simply having the parameters in the wrong order. (my personal guess would be 'send_item_mail [recipient_name] [mail_title] [mail_content] [mail_item] [cash/cod] [mail_type]', though it is most likely wrong).
With all that being said, even if we do manage to get this to not spew errors, as previously mentioned this could simply be a redundant command or red herring.