Has anyone tested an Okta mastered user with a name change and it's impacts to O365 mail flow? I am finding when Jane.Doe@company.com (mailto:Jane.Doe@company.com) becomes Jane.Smith@company.com (mailto:Jane.Smith@company.com), the primary SMTP will update in O365, but Jane.Doe@company.com (mailto:Jane.Doe@company.com) does not write to proxyaddresses in O365 automagically, essentially generating an NDR for anyone using her old address. I am thinking of bringing in proxyaddresses as a synced field, but the challenge of keeping proxyaddresses correct manually could becaome challenging. Anyone figure this out already?
If your Okta tenant is utilizing the enhanced provisioning features this is by design. When these features are used O365 is no longer the source of truth for users. It will be the Okta Universal Directory or in some cases Active Directory via Okta. So in this scenario instead of creating additional SMTP addresses in O365, or O365 doing it automatically when you change the name, it will now expect these settings to come from its new source of truth, i.e. Okta. You are indeed on the right track in planning to bring in the proxyAddresses field and mapping it to O365.
This topic as well as more information on the enhanced provisioning features can be found here, https://support.okta.com/help/articles/Knowledge_Article/Okta-Enhancements-with-Microsoft-Office-365-Integration.