What do you do with previous tenant's/owner's mail... when it's been 18 months+

[Rowellen]

I would bet it's probably just advertising mail that's still coming. Just toss it. That's what we do (and it's been 3 years!).

If it does look like something official, I still return to sender. ETA - it often takes me a few months too

[human bean]

The same is happening to us here, and I do the same as Rowellen. We also get mail for their adult children too which is annoying