[rescbr]

I can't reply to @filoleg's response, but here we go:

> And what’s the other option, running two separate user account management systems in parallel? That’s an insane amount of overhead managing and making sure it actually works.

I've seen a large bank with THREE user account management systems in parallel, and two email systems. And they weren't alone in this way of setting things up.

* IBM RACF, for stuff that touched the mainframe

* MS AD for corporate employees and branch managers, they got Exchange email and Office

* OpenLDAP and some opensource email system for everybody else