If you want to have a claim for recovery of your security deposit, give the landlord notice of your new mailing address within 4 days of moving out. Make sure you can obtain confirmation of delivery of the notice from the post office, as their reluctance to answer the phone or doors may mean you will have to fight them to get your deposit back.
You need to give your landlord notice of your new mailing address within four days after you vacate. This is because the landlord has 30 days to notify you of any claim s/he makes to your security deposit. If you don't give notice of your new mailing address, s/he has no way to give you notice or to return your security deposit.