My colleagues receive emails from "cloud-proactive-comms" with notifications to upgrade our cluster in response to security threats and stuff like that.
How do I register for these emails as well?
First of all, you need to be a project owner in order to receive those emails form "cloud-proactive-comms".
You can also check with your colleague, which permission you are lacking to get those email. As it's possible that your colleague is a Project Owner.
Additionally, if you need RSS feeds available for Security bulletins related to Kubernetes Engine, please visit this article.