It really comes down to; who do you really trust? I personally would create my own self-signed certificate and would simply use that one. This is because I Know I created it and I was not relying on a third-party that could be or will be compromised. So then you would just need to trust yourself;)
So you'll see that all certificates are in /usr/share/ca-certificates. However the default location for certificates is /etc/ssl/certs. You might find additional certificates there.
Best Answer
They're stored here:
I've seen that replacing
omega.contacts.msn.com
's content with this fixes it for me (warning: there could be security implications for this):