I guess "mail from" spoofing is important if you're planning something illegal via the mail (e.g., sending letter bombs or anthrax spores) that could be traced back to you. Otherwise, why bother?
The content of your envelopes remains sacrosanct under U.S. law and the retention period for the tracing scans is limited. I don't even consider this an invasion of privacy if the system is implemented as stated. It's the content of my mail that's private, not the fact that I'm sending it and to whom, when that information is not used unless legally required and destroyed on a rolling basis.
I guess I'm one of those people who privacy absolutists hate because I still treasure and fight for keeping private what I actually consider private rather than trying to keep anything and everything I do absolutely private because that hasn't been possible since before the age of the internet. I worry a lot more about the fact that laws regarding internet privacy are, by comparison to the mails and telecommunications, virtually non-existent and the internet remains the wild, wild west of data collection and mining without an individual's knowledge in a great many cases. I don't mind sacrificing absolute privacy for forms of convenience that I believe are worth the tradeoff but I abhor sacrificing any privacy that I am not aware that I'm sacrificing.
There are trade offs to be made, and neither absolute privacy or absolute lack thereof is actually a tenable situation.
Brian AKA Bri the Tech Guy (website in my user profile) - Windows 10 Home, 64-Bit, Version 1803, Build 17134
. . . the presumption of innocence, while essential in the legal realm, does not mean the elimination of common sense outside it. The willing suspension of disbelief has its limits, or should.
~ Ruth Marcus, November 10, 2017, in Washington Post article, Bannon is right: It’s no coincidence The Post broke the Moore story