Old Tenant Mail Still Coming

[Dewain J.]

Every time I stop by one of my multi family properties, there is a stack of mail addressed to tenants who have long since moved on, and I do not have any information on there new residence. I don't have there new address to go through the forwarding process if I wanted take on that arduous task. Is stamping it Return to Sender sufficient? I don't think that would help with stopping the mail from even coming in the first place which is what I would prefer. Any suggestions on best practices here? 

As far as the mail I've collected, can I stamp return to sender and just drop off at a post office?