I've never tried to do an opt-out for someone else. A few places like dmachoice.org have web forms but I made a lot of phone calls.

There are a couple of local advertisers that are going to send their stuff no matter what I think. I do still get a small amount of junk.

You could try crossing through the address, writing 'no longer at this address, return to sender' on it and dropping it in the out-going mail.

I've been writing "Return to sender, recipient no longer lives at address" on those pieces of mail and re-depositing them in the mailbox. I've been getting less and less of the previous tenants' mail. I think I usually only get one piece a week now.

I do this too, sometimes I put it in a drop box so as to not piss off my carrier. It works eventually.

They just don't care enough to fix their mailing lists. The dead receive a lot of mail.