[p_l]

Binary attachments mostly started to work with less surprises by second half of 1990s, but 8bit unclean issues persisted in my experience... I wanted to say 2001, but I recalled getting hit by them until 2010 at least.

And in some ways desire of people to send non-7bit-ascii text as email is also a continued brokenness in SMTP email.

As for directories - my point was more that directories hid the addressing details from surface UI. Otherwise AFAIK X.400 works perfectly fine without using everything in the possible schema.

Fun fact - Exchange is actually X.400 system, despite no longer having non-SMTP connection options. But its internals are even wonkier, like Exchange and Outlook not supporting HTML Email (no, really, MAPI.DLL crashes on HTML email. If you send/receive HTML email it's stored as HTML wrapped in RTF, and unwrapped when sent elsewhere)