What happens if we already have CrowdStrike, SentinelOne, or a third-party email gateway?

A conflicting EDR agent on the same device as Defender for Endpoint is one of the most common deployment blockers IT Partner encounters. Phase 1 produces a complete inventory of all existing endpoint and email security agents before any onboarding begins. Where a conflict is identified, migration is scoped and sequenced separately — MDE is not deployed to a device group until the incumbent agent is confirmed removed from it.