Windows 7 End of Life
Windows 7 has been end of life since January 14th, 2020. As the result, some software such as Outlook began cease to work. Encryption is always update to improve security. As it update, old encryption became obselete.
Clients facing encryption issue on Windows 7 Outlook can use www.thunderbird.net as mail client or event better upgrade to Windows 10. Use unsupported OS can be potentially dangerous. Although Windows 10 come with native mail client, we also recommend to use Thunderbird on Windows 10. Thunderbird is more stable, lighter, and faster.