I have recently moved into a new apartment (about 4 weeks now) and I keep receiving mail from 3 previous tenants here. I don’t want to recieve them anymore so I’m thinking maybe I should do a “return to sender”. How is that done? Thanks!
can i write “return to sender” and put it in a one of the mail boxes on the street? Would that work or do I have to leave it in my mailbox?

Do I have to write on it in red “return to sender” or how can I indicate it to the post office?

I have mail postmarked July 31. Does that mean he/she put it in the mail the 31st? Is it possible that he/she put it in the mail on the 27th or 28th?