Who relies on this stuff?
Does it only affect the encrypted data or does it affect messages that are simply signed by PGP (or S/MIME?)
I've only been using email for about 24 years and can't remember ever coming across anybody that encrypted their emails. I recall playing with it for a few minutes back in the 90s but that's as far as I got. Though I have seen many emails (mainly security or open source related mailing lists and stuff) that had PGP/GPG signatures(or so they claimed I have never tried to validate any of them).