TLS Protocol Version 1.0 is not secure and as a result, needs to be disabled on servers that offer PCI compliance.
If you’re using Windows 7 and Windows 8.0, applications built using WinHTTP such as Microsoft Outlook, Word, etc will only support TLS 1.0.
Since this protocol is no longer secure and is now disabled if you try and establish a secure connection using your Outlook e-mail client, Outlook will display an error message similar to the one below:
To resolve this issue and allow Outlook to communicate securely using TLS 1.2, you will have to follow these instructions.
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.
If Outlook is still not able to send or can't connect to port 465, change to port 25.