Please consider that we haven't tried the following instructions for Outlook 2007, 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.
If Outlook is still not able to send or can't connect to port 465, change to port 25.
NOTE: If you are not confident editing the Windows registry keys, please open a support ticket and we will provide you with a .reg file which will add the keys for you.