If no Ingress/Egress is defined for all pods in a namespace then there is a high chance of unauthorized workloads communicating the pods of other namespace.
To ensure outside malicious traffic is not allowed to connect to pods of a particular namespace. It is recommended to configure a NetworkPolicy, use 'podSelector:matchLabels' to attach it to pods, and include 'policyType:Ingress/Egress' for the same NetworkPolicy.