We have a hybrid Exchange environment with Exchange 2010 and a small number of mailboxes migrated to Exchange Online. We are using ADFS for authentication.
However, for mailboxes that have been migrated to Exchange Online, the Outlook 2013 autodiscover process fails.
Oddly, Outlook 2016 autodiscover works fine. Autodiscover also works fine for on-premise mailboxes. Users can authenticate to Outlook web fine via ADFS.
Outlook 2013 seems to have a problem at the point it is redirected to https://autodiscover-s.outlook.com/autodiscover/autodiscover.xml (normally the final step after first contacting on-premise CAS server). It then shows a logon prompt, however no credentials are accepted. If credentials are provided, they fail with 0x80004005. Screenshot below.
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