Outlook connects to your primary mailbox in an on-premises Exchange server by using RPC, and it also connects to another mailbox that's located in Office 365.
You migrate your mailbox to Office 365 from an Exchange server that Outlook connects to by using RPC.
In these scenarios, you may be prompted for credentials, and Outlook doesn't use Modern Authentication to connect to Office 365. After you enter your credentials, they are transmitted to Office 365 instead of to a token.
Create the following registry key in order to force Outlook to use the newer authentication method for web services, such as EWS and Autodiscover.
- Exit Outlook.
- Start Registry Editor. To do this, use one of the following procedures, as appropriate for your version of Windows:
- Windows 10, Windows 8.1 and Windows 8: Press Windows Key + R to open a Run dialog box. Type regedit.exe, and then press Enter.
- Windows 7: Click Start, type regedit.exe in the search box, and then press Enter.
- In Registry Editor, locate and then click the following registry subkey:
- On the Edit menu, point to New, and then click DWORD Value.
- Type AlwaysUseMSOAuthForAutoDiscover, and then press Enter.
- Right-click AlwaysUseMSOAuthForAutoDiscover, and then click Modify.
- In the Value data box, type 1, and then click OK.
- Exit Registry Editor.
3114349 December 8, 2015, update for Outlook 2013 (KB3114349)
3114333 December 8, 2015, update for Office 2013 (KB3114333)
Note Office 2016 does not require an update for this registry key to work.