MicrosoftThis change reveals a huge design flaw in the admin web gui: you do not use the displayname everywhere when you, eh, display(!) accounts. If you did, this wouldn't be any problem at all.
displayName is hardly unique, even if it is more helpful than a GUID. To guarantee uniqueness we've historically used "displayName (sAMAccountName)" as our cn/rdn on-premises, and the sAMAccountName always matches the mailNickname/alias for Exchange. The problem Microsoft tried to fix with this change was apparently syncs from multiple domains where the uniqueness couldn't be assured, but instead of throwing an error like the Entra ID Connect Sync process has always done for other collisions (i.e. email address assigned to another recipient), they came up with this kludge which didn't account for how OWA and other interfaces use the data. I'm generally a fan of Microsoft's tech but this remains one of the most ill-conceived steps they have ever taken and not immediately taken action to revert or correct after running into reality. This is what agile development brings, and data architecture is not agile.
