This may be automatically fixed in one of Microsoft’s Optional Windows Updates, but here is the quick fix.
If you get a Windows 7 Email Authentication issue when using secure settings we may need to enable TLS. So far this worked for one user.
You can do it via screen connect. Connect in and transfer and extract this ZIP file and double click the .reg file to import it into the Windows 7 registry. Then reboot the computer.
Microsoft Info: https://support.microsoft.com/en-ca/help/3140245/update-to-enable-tls-1-1-and-tls-1-2-as-default-secure-protocols-in-wi