Is that actually true today? When I was doing EDI stuff ~20 years ago, it was mostly done using FTP, with some forward-thinking orgs moving to SFTP or (HTTPS-based) AS2.

I see that Wikipedia claims that "X.400 is quite widely implemented[citation needed], especially for EDI services", and that might once have been the case - but I doubt it was particularly widespread even at the time that article was first written. It's worth noting that that [citation needed] tag dates from October 2008!