If Outlook clients are not autoconfiguring after a BitTitan cutover, the issue may be that Autodiscover for the destination tenant is not resolving correctly.

Outlook relies on Exchange Online Autodiscover to find the right Exchange endpoint and build the user MAPI profile. After a BitTitan cutover, users need Outlook to recognize that their mailbox now resides in the destination tenant so the profile can be reconfigured. When Autodiscover for the destination tenant domain does not resolve properly, Outlook cannot complete that change automatically.

Exchange Online Autodiscover follows a specific DNS lookup chain that ultimately reaches the Microsoft-hosted Autodiscover endpoint. If you have custom Autodiscover CNAME records pointing to third-party filtering services or on-premises Exchange CAS servers, Outlook may discover the wrong endpoint for the destination tenant.

Ahead of cutover, confirm that Autodiscover for the destination tenant domain resolves to the correct Exchange Online Autodiscover endpoint. Use the Microsoft Remote Connectivity Analyzer to test the destination tenant Autodiscover configuration. Misconfigured Autodiscover often shows up as Outlook profile failures that appear to be a BitTitan issue, but are actually caused by DNS.

Have you validated Autodiscover resolution for the destination tenant domain before your BitTitan cutover date?

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