Little known fact: almost all of the spam (at least in my area) is not postal delivery. Private couriers deliver it. You can affix a "pas de pub" (no ads) sticker to your mailbox, and it stops. (It's possible the post also stops some spam delivery with this notice)
Canada Post delivers junk mail to my private mailbox. Changed my bills to online (for those I could) and posted letter-stickers to my mailbox saying "No Admail Please" and now I get 0 spam mailings. Also opted out of CMA marketing, including opting out former residents addresses.
I havne't received junk mail in over a year.