USPS will forward only First Class mail - not junk mail/presort. They will forward magazines for 90 days.
We use
MyRvMail. They will set up a PMB for you and then you put in a forward request with USPS to have your mail forwarded there. Mail accumulates until you tell MyRVMail where to send it.
GoodSam members get a discount.
You can go on line and view what mail is in your box and tell them to shred anything you don't want forwarded to you.
We only change the address on our magagzine subscriptions to the MyRvMail address since we're gone longer than 90 days USPS will forward. We also change the address for our on-line meds so that is sent directly to our MyRVMail address.
If you really need every piece of junk mail, USPS has a weekly forwarding service. It's a little pricey.