One of the hilarious exchanges (pun intended) that happened on Sinofsky's blog concerned MS Exchange. The executive-level view of events is vastly different from the actual events.

tl;dr:

Stevesi (Technical Assistant to BillG): Mgmt forced Exchange to use NT Directory (followed by glowing description of the NT directory)

DonH (Exchange Directory dev lead/ later Active Directory dev lead): No, NT was late, and eventually canceled NT Directory. Exchange wrote and shipped our own Directory and then moved the code to NT to use as the base for Active Directory.

Stevesi prevaricating about high-level executive view of the interaction of NT vs Exchange directory.

DonH: No, that's wrong. NT provided nothing. Exchange created an email-specific directory. I used that to make Active Directory. Water flowed uphill not downhill.

from https://hardcoresoftware.learningbyshipping.com/p/021-expand...:

"That proved to be a defining moment because deploying a directory was hugely complex and there was no way EMS could do it twice. In one of the rare times an architectural choice was pushed to a team, using the directory from NT became a requirement for EMS. Many others supported this, including the Server leadership. It was to them as natural as pushing Excel to use Windows—the directory was that core to NT Server—while sharing files and printers was the baseline scenario, it was the directory that brought deep enterprise value to customers. For the better part of the following year or more, EMS would not speak well of using the NT Directory, and conversely the NT team felt that EMS was trying to use the Directory in ways it was not designed to be used. This sounded to me a lot like getting Excel to work on Windows, and it played out exactly that way. Had EMS not used NT Directory, it is likely Directory never would have achieved critical mass as the defining app for the client-server era (and remained the cloud anchor for today’s Office 365). And conversely, had the NT team not met the needs of EMS, then the NT Directory would have likely been sidelined by the rising importance of the email directory in EMS. Forcing this issue, while it might be an exception, only proved the strength of a strategic bet when it is made and executed. Still, it was painful."

Comment from DonH Apr 22, 2021, at end of blog entry:

"Speaking as the dev lead for the Exchange Directory (1991-1996) and later on Active Directory (1996-2005), there's a lot wrong with this chapter. NT's approach to functional directory services in the early 90's was "wait for Cairo. they're building one", which meant that we in Exchange had to build our own directory service. When Cairo collapsed (late 1995) Exchange and NT struck a deal so that once Exchange 4.0 shipped (April 1996) one of my developers and I brought a copy of the Exchange Directory source code over to Windows, and we built Active Directory out of that. Exchange in no way "bet on" the NT Directory; we essentially built the replacement for it in order to get the features we needed. Ask me if you need details.

However, the part about endless repeated pressure to build everything (specifically including the directory) on top of SQL is entirely accurate.

I'm only moderately annoyed that I had to pay ten bucks to post this correction."

Second comment from DonH:

"You're missing the point that there was no NT Directory. The strategy given to us was "use the NT directory, which is the Cairo directory. Sorry that doesn't exist yet, so Exchange might need to cobble something together for its first release." I built that something, and later went on to use it to fill the directory service shaped hole in Windows.

Presenting this as Exchange leveraging the NT Directory might be polite, but it is definitely not accurate.

And although I remain eternally grateful to LDAP for saving me from COM I completely agree about omitting it from the history."