public boolean storeLetter(ItemStack letterstack) {
ILetter letter = PostManager.postRegistry.getLetter(letterstack);
// Mark letter as processed
letter.setProcessed(true);
letter.invalidatePostage();
NBTTagCompound nbttagcompound = new NBTTagCompound();
letter.writeToNBT(nbttagcompound);
letterstack.setTagCompound(nbttagcompound);
this.markDirty();