Proper way to return mail from previous occupant in apartment?

I have mail in my new apt from the old occupants. Whats the proper thing to do? Leave it in the post box? Take to post office? Drop off at leasing office?(I know they should have fwd address, but are they bound by law to fwd mail, or can they pitch it?). Getting these stray letters have me wondering if I still have things going to my old address, even though I put in a change of address? I probably shouldn't care, but the packages look important and I want to make sure they get to the right person.

Cross out the address and write "Not at this address." Drop off at post office, give to carrier, hang on your mail box for pick up.

It is not the leasing office's job to forward. The former tenant should have left a forwarding address with the post office.

Write "no longer at this address" on the packages and letters and give them to the post office. They will forward them on if the previous occupants left a forwarding address. If not they will return to sender.

put it in the outgoing mailbox

bring it to the post office and tell them they will stamp it return to sender due to address change. if you leave it in the mail box it'll obviously come back to you lol

As a person who has moved 18 times in 26 years it is a problem I often encounter. It is easy- let the post office handle it by you crossing out the person's name, just put a single line through it and in Capital letters write no longer at this address, circle the address. Put it back in the mailbox or in any mailbox and it goes back through the postal system where they might find the new address. No need to put a stamp on it!

just write not at this address or RTS (Return to Sender) so it goes back to the person or company that mailed it.