On-premises Lync Server integration with Exchange Online fails

When you deploy on-premises Microsoft Lync Server 2013 or Microsoft Lync Server 2010 integration with Microsoft Exchange Online, the integration fails, and you experience the following symptoms:

• When you right-click the Lync icon in the system tray next to the clock and then click Configuration Information, the status�of the EWS Information�item is displayed as�Not Deployed. When this is the case, the Lync client can't check the Calendar or out of office (OOF) information by using Exchange Web Services (EWS).
• The Lync client Autodiscover process for the Exchange Online server fails.

Important�Follow the steps in this section carefully. Serious problems might occur if you modify the registry incorrectly. Before you modify the registry,�back it up for restoration� in case problems occur.

Warning Serious problems might occur if you modify the registry incorrectly by using Registry Editor or by using another method. These problems might require that you reinstall the operating system. Microsoft cannot guarantee that these problems can be solved. Modify the registry at your own risk.

To resolve this issue, add the OverrideDirectHttpConnection�registry key, and then configure it so that the Lync client won't try a direct HTTP connection. To do this, follow these steps::

1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then click the following registry subkey:
   
   For Lync 2010:
   HKEY_CURRENT_USER\Software\Microsoft\Communicator\
   For Lync 2013:
   HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Lync\
3. On the Edit menu, point to New, and then click DWORD Value.
4. Type OverrideDirectHttpConnection, and then press Enter.
5. Right-click OverrideDirectHttpConnection, and then click Modify.
6. In the Value data box, type 1, and then click OK.
7. Exit Registry Editor.

This issue occurs when the following conditions are true:

• A firewall is configured to block internal client computers (end-users on Lync) from making direct connections to the Internet over HTTP port 80 and HTTPS port 443.
• The proxy settings in Internet Explorer are configured to redirect all traffic that's trying to go out over port 80 or 443 through the proxy server. However, instead of using the proxy settings that are defined in Internet Explorer, Lync tries to connect directly through Exchange to autodiscover.contoso.com�over port 80 or 443.�
  
  Note�The placeholder�Contoso.com�represents the domain that you use for your organization.
  
  The firewall blocks this direct connection attempt, and by the time Lync tries to fall back to use the proxy server, the request times out. Therefore, we have to force Lync to use the proxy first.

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