Attorney-Client Privilege in the Cloud: Securing Microsoft 365 for Law Firms

Privilege is a control problem, not just a legal one

Attorney-client privilege protects confidential communications — but courts look at whether a firm took reasonable steps to keep them confidential. In a cloud-first practice, "reasonable" is increasingly defined by your Microsoft 365 configuration, not your engagement letter. ABA Model Rule 1.6(c) makes the duty explicit: lawyers must make reasonable efforts to prevent unauthorized disclosure of client information.

The configuration that protects privilege

• Conditional Access enforcing MFA on every account and blocking legacy authentication — the single highest-impact control against credential theft.

• Sensitivity labels with encryption applied to matter files, so a forwarded document stays protected outside the tenant.

• Data Loss Prevention rules that catch client identifiers and matter numbers before they leave by email.

• Audit logging retained long enough to reconstruct who accessed a matter, and when — the record you will want if a breach is ever alleged.

• Ethical-wall enforcement via security groups, so conflicted personnel cannot reach a matter at all.

Where this connects to the rest of your stack

The same controls that protect privilege also satisfy the cyber-insurance and breach-notification expectations we cover in our security & compliance posture. If you want a structured read on where your firm stands, our free Security Risk Assessment walks the major control families in about ten minutes.

How we approach it for law firms

We treat the Microsoft 365 tenant as part of the privilege perimeter — configured, monitored, and evidenced. See how we work with legal practices, or talk to us about a tenant review.