macOS Mail's API to AppleScript or Automator to export a mailbox

[Mac2013orlater]

OS X 10.9 Mail's GUI function (guess for 10.10 it looks same way):
Mailboxes plane >>> select a mailbox >>> context menu >>> Export Mailbox...

One was on the search for equivalent Mail's API - AppleScript scripting or Automator.
No findings.
It seems it was not possible currently to automate mailboxes export to a disk file as
the GUI function described above does it in interactive mode.
Are these the real facts indeed?

 

[Mac2013orlater]

Automator - recording mode is the only option I found to accomplish the addressed task.