After updating a Dynamics 365 (online) organziation to version 9.0 the Dynamics 365 for Outlook client is unable to connect.
A Dynamics 365 (online) organziation on version 9.0 requires TLS 1.2.
Microsoft has released Dynamics 365 for Microsoft Outlook version 9.0 update. This update includes support for Transport Layer Security (TLS) 1.2.
Version 9.0 of Dynamics 365 for Outlook is available at the link below and is the recommended client to use for connecting to 9.0 organizations: