Hello Experts. I am in the process of testing Email Migration to Office 365. On-prem we have, Exchange 2013 CU19, with AD 2012R2. i have enabled modern authentication, and Seamless Sign on. and i have set up Pass-through authentication, and we have Exchange hybrid configuration setup with centralized mailflow, and using Outlook 2016.
The issue I am facing is: when I migrate a user from from on-prem to the cloud, they get a prompt saying the exchange admin has made changes, and they need to restart their outlook. when the migrated user closes and re-opens his Outlook, Outlook prompts them for credentials. this only happens once. after inputting their credentials, they do not receive anymore auth prompts when opening outlook.
My question is, why does the user get prompted for these credentials at first time, after they open outlook again after migration? shouldn't modern auth handle this?, modern auth/ SSO works fine with skype, and OWA. i also noticed, the users credentials are not cached in credentials manager, and after inputting their credentials in Outlook, that stores the credentials in credentials manager, along with what looks like access tokens.
I also tested by inputting the users Outlook credentials into credentials manager manually prior to migration. then after migration, and after they restart their Outlook, they do not receive an authentication pop up from Outlook. why doesn't Modern auth handle this itself, and why are the users Outlook credentials not being cached into credentials manager?
Please let me know, and thanks in advance.