Presorted first class mail can be junk mail but it's not always junk mail.
Some school newspapers, bills and magazines that you order can come in presorted first class mail and not be junk mail.
The majority of presorted first class mail is junk mail but not all of it is.
The cost for presorted mail is 44 cents per ounce but as the weight increases the presorted postage costs goes up some.
For example if you're mailing presorted mail of 3 ounces then the cost is 78 cents for the 3 ounces of presorted mail.
Presorted Postage is mail that has been sorted already by the sender and they've already paid for cheaper postage to mail that presorted mail.
Presorted mail can be in the form of sales papers, coupons, magazines, bills etc.
The presorted postage for a business is much cheaper than regular stamps because the USPS does not have to do the sorting of the mail beyond sorting it to arrive at the correct address.
If you're a business and send a lot of mail out then using presorted postage with a permit for the postage can save you a lot of money.
You need to presort the mail you're sending out and some presorted mail just goes to any address available such as flyers, sales papers, school newspapers, etc.
While some mail such as bills are addressed to a certain person or business they are sending the presorted postage mail too.