I got a book marked postage due which my postal carrier delivered to my door. I didn't have the change on me to pay her with at the time, and I haven't seen her since, so can I leave the  $ in an envelope with her name on it in my box?

Also, can I leave her a bag of cookies in my box also?

Thanks

Yes, you can do both. I would put either the carriers name (if you know it) or the carrier for (your address) and the city state and zip. Some carriers don't always look at outgoing mail closely, so then if it gets in with all the mail it will end up in the right place.