I've done this and it makes a big difference, but I still get a lot of junk from local businesses. Either those businesses are not part of the DMA, or they are ignoring the opt-out list. I'm not sure what to do about it.
I recall reporting this to the USPS multiple times without any effect. The only thing that helped was putting a note inside my mailbox to check for my neighbor's mail.
> I'm not sure what to do about it.
What I found to be particularly effective when dealing with spam from local businesses is to contact them directly and request that your information is deleted, while also posting that they engage in unscrupulous practices like sending junk mail on public review sites like Yelp and Google Reviews, and then finally filing a BBB complaint directly against the business.
Also as I recall, there was a coupon mailer that did not participate in the DMA. The flyers show up with branding from Vericast/Save/Valassis. The opt out for them is here: https://www.save.com/mailing/delivery-options
Similarly I recently moved houses and got a ton of catalogs to the former owner. It was a PITA to get sorted out, but after a couple months of diligent removal requests my mail is mostly stuff I care about.
Then this would be the organization's problem to keep their own lists up to date. I realize this is probably infeasible but it would be nice.