Thanks Jeremy! I guess you rightly pointed that out there is no way to change ‘proxyAddress’ since it gets populated internally by Entra. And changing anything manually is not acceptable and won’t solve the issue.
Also, to put in context, this is our sandbox environment and currently we are just required to populate email address in Entra. But ‘proxyAddress’ won’t let us do that and Entra admins not too keen on making any changes to it.
I guess, the pattern/generator that I posted in my initial post, will work fine for AD but not for Entra because in Entra SMTP, UPN and mailNickName all get propagated to proxyAddress field by default (don’t think they will change that and ideally it shouldn’t be). Now when ISC tries to generate a unique email, ISC checks for the uniqueness with proxyAddress too (not sure if it should be that way and I have limited knowledge/understanding of the technicals or working of Entra). Found this while browsing through Entra docs. This tells how proxyAddress is populated in Entra- How the proxyAddresses attribute is populated in Microsoft Entra ID - Azure | Microsoft Learn .
Also, as mentioned above, the uniqueCounter in our pattern may work for AD but not for Entra. Same pattern/generator has worked for others too. Reference - Email uniqueness in AD - #9 by MVKR7T
The only possible solution that I can see now (for our case) is, writing an AttributeGenerator rule for Entra’s mail attribute. - How to Search Non-Indexed Account Attributes in IDN Rules for Uniqueness - Compass