wow, how to romanticize X.400 ...

- poor Internet fit, assuming managed, trusted networks - some promises depended on all participating systems behaving honestly

- once a message reaches another server, you cannot guarantee it isn't copied, backed up, or logged

- X.400 read receipts: more reliable but also more privacy invasive

- X.400 metadata: carries a lot of routing, classification, and organizational info leading to potential privacy leaks

- SMTP is ugly but observable, you don't need a standard specialist to debug issues