[Flimm]

Actually, even PGP is not fine for high security scenarios. For example, it doesn't encrypt headers, including the subject line, which I would say is just as important as an email's body.

[hannob]

Some people are trying to fix that: https://modernpgp.org/memoryhole/

[capt_hotpants]

Good point.

S/MIME might also have some dependencies on PKI that in some scenarios could make it unsuitable for high security scenarios?