Do I need Microsoft 365 E5 for Zero Trust?

Not necessarily as a starting point. Microsoft 365 E3 gives many organizations a credible first phase for Zero Trust by supporting core identity and device controls, basic policy foundations, and an initial security baseline. Microsoft 365 E5 usually becomes relevant when the roadmap requires more advanced capabilities such as stronger identity protection, Privileged Identity Management, broader Defender XDR coverage, and richer data protection controls. In other words, E5 is often the cleanest path to a more complete posture, but Zero Trust maturity still depends on implementation and governance, not licensing alone.