Please consider that we haven’t tried the following instructions for Outlook 2003/2007/2013, if you are using this version released around 10 years ago you should consider upgrading to a newer version.
Follow the instructions below:
a) Update Windows 7/8 using Windows Update and download/install all important updates. For windows 7 is important that you install Service Pack 1.
b) Install KB3140245 and reboot: http://catalog.update.microsoft.com/v7/site/search.aspx?q=kb3140245
c) Execute the EasyFix and reboot: https://support.microsoft.com/en-us/help/3140245/update-to-enable-tls-1-1-and-tls-1-2-as-a-default-secure-protocols-in
d) Start > Search for Execute, Type Regedit and press Enter to access Windows Registry.
Check this registry key: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\Schannel\Protocols
Under the Protocols key, add two new keys, if not already there: One called “TLS 1.1” and one called “TLS 1.2“. Inside both of these keys, add another key called “Client“. Now create a DWORD value in each Client key called “DisabledByDefault” whose value is 00000000.
Reboot and start Outlook.