// Prepare the letter
ILetter mail = new Letter(this.address, letter.getSender());
mail.setText("Please find your order attached.");
for (int i = 0; i < ordersToFill; i++) {
mail.addAttachment(inventory.getStackInSlot(SLOT_TRADEGOOD).copy());
}
mail.addAttachments(getSurplusAttachments(ordersToFill, letter.getAttachments()));
// Check for necessary postage
int requiredPostage = mail.requiredPostage();