I don't blame you, I would be livid too.

I agree, and would try to talk to the postal inspector and
see if they can work something out, by leaving
an official letter at your neighbors house and also on the cars. Their has to be something you can do, maybe even contact your local coucilman and see if they can put a red painted curb right
in front of your mail box. Than if a car parks their they
can get a parking ticket.

Good luck and let us know what happens.