Exchange Admin Improvements Announced at Microsoft Ignite 2019

Kevin Mychal Ong I noticed some time ago that ExternalDirectoryObjectId is actually stored as a string rather than a Guid, unlike most of the other Guid properties:

>Get-Mailbox | Get-Member -Name ExchangeGuid

   TypeName: Deserialized.Microsoft.Exchange.Data.Directory.Management.Mailbox
Name         MemberType Definition
----         ---------- ----------
ExchangeGuid Property   System.Guid {get;set;}

>Get-Mailbox | Get-Member -Name ExternalDirectoryObjectId

   TypeName: Deserialized.Microsoft.Exchange.Data.Directory.Management.Mailbox
Name                      MemberType Definition
----                      ---------- ----------
ExternalDirectoryObjectId Property   System.String {get;set;}

So my guess is -Identity is set to accept [string] objects and has a few aliases (UserPrincipalName, ExternalDirectoryObjectId) and either ValidateScript/ValidatePattern or some later logic figures out what was supplied.  Identity too is likely the first declared parameter in the default set.

I'm just speculating on that stuff though.  I've tried a few different ways to create my own -Identity parameters on scripts and have wondered what / how MS might get it done.