It probably wouldn't help you escape email ads though, the USPS is heavily funded by bulk mail.
Then again, they allow mail that fraudulently tries to appear "official" or important when it's just an ad (and sometimes an outright scam!) so all that would have to be legislated to ensure it happens, I suppose. Would love to see "mail system reform" on a party platform, but I guess that doesn't get the voters out.
I disagree, based on accounts by librarians that they're becoming tech support of last resort for various unaccountable and uncaring email providers that the most vulnerable in society are trying to use just to get by, causing basically everyone involved to be miserable and worse-off than they might be in a better-functioning system.
I don't think government should be the only provider (and I don't think I even implied that?) but do think that if one of the main ways of interacting with vital government and private-sector services is going to be email—and it is—then it makes a lot of sense for the USPS to provide a viable option for that, for basically the same reason that it makes sense to have a USPS at all.
It's nigh-necessary for communicating with government and participating in the economy—USPS ought to do email.