This is similar to this topic for gmail: https://www.ritlabs.com/en/forums/forum4/topic7101/

Basically you need to go to https://www.digicert.com/digicert-root-certificates.htm and download certificates "digicert assured id root ca" and "digicert assured id ca-1". Install the certificates using the instructions of the link above and you probably need to add the root certificate to trusted. After this all should be fine