Re: Internet-Email is so much simpler than X.400.
Reducing complexity (and reducing the size of the attack surface) is generally a Good Thing from a robustness and security point of view.
That said, Internet email may have been simpler than X.400 back in the day when X.400 was the Next Big Thing, but in the real world the "simplicity" of Internet email from that era has long gone, to be replaced by a nightmare collection of unarchitected bandaids and patches trying to build security on something that fundamentally isn't trustworthy and is barely fit for purpose in today's environment.
X.400 and friends were architected, designed, and built to do exciting 'modern' stuff like compound documents, to support a character set with more than USASCII characters, to do stuff like trustworthy documents and trustworthy identities and trustworthy proof of delivery etc - these things were fundamental to the design, not bolted on as afterthoughts. So X.400 etc was inevitably more complicated than the teletype-era protocols POP/SMTP (and their dependencies) were back then. That extra complexity also required more compute power, which back then wasn't readily available at low cost like it has been for many years.
Nowadays the need for trustworthy email has massively increased, while the cost of the necessary compute power has massively decreased. But courtesy of the commodity internet "service" providers and others, most of us are stuck with the email architecture of the 1970s, plus the band aids and elastoplasts that attempt to make it workable in today's untrustworthy world.
Further reading: see e.g.
https://www.isode.com/whitepapers/x400-messaging.html
Alternatively: to fail to plan is to plan to fail. Internet email wasn't planned to be the way it has ended up, and it shows. X.400 was planned, designed, and implemented, but internet email was simpler **at the time*. Sometimes it's best to accept that something is no longer fit for wide usage.
Complexity is bad in general. There may be good reasons to add some complexity, and X.400 and friends address many of those from the ground up.
Without a _really_ good justification you shouldn't attempt to force-fit a toolset into an environment which would be better served by a different toolset, even if it means abandoning the 'cheap' legacy toolset.
Biting the hand that feeds IT
