In 99, webmail providers were nearly all using squirrelmail or some self-invented thing and people were using offline mail clients, where GPG/PGG could have been an option. The terminals were behind, cloud computing ahead, and everyone knew your stuff is gone if your are careless and reinstall your computer, since POP3 was still a common thing. (Unlike IMAP, POP is usually used in a mode where no copies are left on the server, so the mails only exist where you pulled them down to.)
The big difference, however, that the world wasn't yet spying on every drop of text you made, and that is why email encryption didn't take off: there was no real need.
Unfortunately, the cloud and web "revolution" happened before people realized they should encrypt _before_ moving back to centralized services and now it seems to be a lost cause.
No. I don't know if it's a generational thing, but people on message boards today seem pretty convinced that Snowden invented concern over dragnet encryption. Get a copy of Applied Cryptography and thumb through it; it's shot through with the mindset that NSA (specifically: NSA) is reading all your mail. The 1990s were the decade of the cipherpunks, the Clipper Chip, the crypto wars, Echelon, and the hacker crackdown. More people encrypted their email then than do now.
But NSA - I really hope - doesn't sell your data for profit to insurance and medical companies, so there's a difference. If NSA picks up something serious about you, you're in deep trouble, but the current data sniffer companies can make your life really hard without you even realizing it.
I'm not advocating plaintext email. I'm advocating for no email. But since it'll be 10-15 years before email takes its place alongside ICQ among protocols normal people never use, in the meantime, the right solution is to keep email banal, and keep sensitive stuff on secure messaging protocols.
The big difference, however, that the world wasn't yet spying on every drop of text you made, and that is why email encryption didn't take off: there was no real need.
Unfortunately, the cloud and web "revolution" happened before people realized they should encrypt _before_ moving back to centralized services and now it seems to be a lost cause.