TLS 1.0 and 1.1 protocols have become obsolete and are no longer supported by most applications due to having vulnerabilities. Outlook will require TLS 1.2 to be enabled in the Windows settings, any version of Outlook may stop working on the workstations that do not have TLS 1.2 support enabled.

Windows 10 is not affected since it has TLS 1.2 already built-in, but previous versions may need to be upgraded to have TLS 1.2.

If TLS 1.2 is not enabled on the workstation, Outlook will show the following error upon checking mail:

Check if TLS 1.2 Is Enabled

To check if TLS 1.2 is enabled on a computer or not:

  • Click the Windows button in the left lower corner and type “Internet Options” and select it
  • Click on the Advanced tab and scroll down to the "Use TLS 1.2" and make sure it is checked

If TLS 1.2 is not on the list or is greyed out, a Windows update should be downloaded and installed on the computer.

Note: Please see the link below to enable TLS 1.1 and 1.2 as default secure protocols.

Update to enable TLS 1.1 and TLS 1.2 as default secure protocols in WinHTTP in Windows

Check the System Type

To install the proper update, you will need to check the system type.

  • Open File Explorer, right-click Computer, and select Properties.
  • New window with system information will open. System type can be found there.

Download Windows Updates

Download and install the corresponding Windows update by following this URL: https://www.catalog.update.microsoft.com/search.aspx?q=kb3140245

Note: the update for x32/x86 systems is listed as just “Update for Windows 7 (KB3140245)”.

After the update is installed, check if TLS 1.2 is enabled again as described in first steps of this instruction.