Increase the number of retries when WinHTTP tries to connect to a host in Outlook 2013 and Outlook 2016

By default, Microsoft Windows HTTP Services (WinHTTP) will try six IP addresses (one initial attempt and five retires) to establish a connection to a host. However, if Microsoft Outlook 2013 and Outlook 2016 try more than six IP addresses, the connection will fail. This is particularly true on networks that have intermittent IPv6 connectivity problems. The increase of the number of retries makes sure the success of the connection by using IPv4 addresses. To enable this feature, install the following updates and then follow the steps.

For Office 2013, install Description of the security update for Outlook 2013: April 11, 2017 and Description of the security update for Office 2013: April 11, 2017.

For Office 2016, install Description of the security update for Office 2016: June 13, 2017 and Description of the security update for Outlook 2016: June 13, 2017.

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

1. Exit all Microsoft Office applications.
2. Start Registry Editor:
   • In Windows 10, go to Start, enter regedit in the Search box, and then select regedit.exe in the search results.
   • In Windows 8 or Windows 8.1, move your mouse to the upper-right corner, select Search, enter regedit in the search text box, and then select regedit.exe in the search results.
   • In Windows 7, select Start, enter regedit in the Start Search box, and then select regedit.exe in the search results.
3. Locate and then select the following registry subkey:
    
   Outlook 2013
   HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\15.0\Outlook\HTTP
   
   Outlook 2016
   HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Outlook\HTTP
4. On the Edit menu, point to New, and then select DWORD Value.
5. Enter MaximumConnectRetries, and then press Enter.
6. In the Details pane, press and hold (or right-click) MaximumConnectRetries, and then select Modify.
7. In the Value data box, enter 1, and then select OK.
   
   Note Outlook 2013 and Outlook 2016 use this value to set the number of WINHTTP_OPTION_CONNECT_RETRIES for requests when MAPI/HTTP connections are used.
8. Exit Registry Editor.