Microsoft 365 (M365) security for legal and accounting firms needs to protect more than email, files and logins.
It needs to protect the trust the firm has already earned.
The issue is the M365 default security gap: the space between what Microsoft 365 can do and what has actually been configured for the firm. Default settings are convenient, but they are rarely enough for a legal or accounting practice handling confidential client data.
This guide breaks down the core controls firms should understand: conditional access policies, multi-factor authentication enforcement, data loss prevention, Azure security, eDiscovery readiness and legal professional privilege compliance.
For firms weighing security frameworks alongside Microsoft hardening, SIAX’s guide toISO 27001 vs Essential Eight for Financial Services gives a practical comparison of what each framework asks of an organisation.
Understanding M365 & Azure Security Challenges in Legal and Accounting Firms
Professional services firms carry a different security burden from many other businesses.
What Legal Firms Need to Protect
Legal firms may hold:
- Privileged communications
- Matter files
- Litigation materials
- Contracts and deeds
- Settlement documents
- Family law records
- Employment and workplace files
- Merger, acquisition and commercial transaction documents
The issue is not only unauthorised access. It is also accidental disclosure, excessive internal access, uncontrolled sharing and poor record handling.
What Accounting Firms Need to Protect
Accounting firms may hold:
- Tax file numbers
- Bank account details
- Payroll information
- Business activity statements
- Financial statements
- Client advisory notes
- Source documents
- Identity verification material
For tax practitioners, the obligation to keep proper client records gives security and retention a practical compliance dimension.
The M365 Default Security Gap: Secure Platform vs Secure Configuration
Microsoft 365 includes strong security capabilities. That does not mean every tenant is secure by default. This is the M365 default security gap.
The Australian Signals Directorate’s Blueprint for Secure Cloud focuses on the design, configuration and deployment of secure cloud and hybrid workspaces, with Microsoft 365 as a current focus.
Common Gaps in M365 Environments
Typical issues include:
- MFA enabled for some users, not all users
- Administrators using everyday accounts for privileged work
- Legacy authentication still permitted
- External sharing settings left too open
- Guest access unmanaged across Teams and SharePoint
- Sensitive documents stored without labels
- DLP policies missing or too broad
- Retention settings applied inconsistently
- Audit logs available, yet rarely reviewed
- Old users, groups and permissions left in place
None of these require exotic attack methods. They are configuration and governance issues.
If your current provider is responsible for Microsoft 365, identity, endpoints and support, this guide onHow to Choose a Managed Service Provider in Melbourne Without Lowering the Standard is a useful next read.
Conditional Access Policies: Controlling Who Gets In, From Where, and Under What Conditions
Conditional access policies are one of the strongest controls available in Microsoft Entra ID.
In plain English, they decide whether a person can access a resource based on specific signals. Those signals can include who the user is, where they are signing in from, what device they are using, which application they want to access and whether the sign-in appears unusual.
Microsoft describes Conditional Access as a way to apply access requirements such as conditional access policies and multi-factor authentication requirements when users access resources.
Useful Policy Examples
A firm may configure policies that:
- Require MFA for all users
- Require stronger authentication for administrators
- Block legacy authentication
- Require compliant devices for sensitive applications
- Restrict access from specific locations
- Block or challenge risky sign-ins
- Limit browser sessions on unmanaged devices
- Require approved apps for mobile access
These are practical controls that strengthen access without blocking legitimate work.
Keep Policy Design Practical
Poorly planned access controls can interrupt legitimate work. That is why conditional access should be tested, staged and reviewed.
For legal and accounting firms, the aim is controlled access that supports real workflows: court, client meetings, remote work, audit periods, tax deadlines and partner approvals.
Multi-Factor Authentication Enforcement and Identity Hardening
Identity is usually the first place to harden.
If an attacker gains access to one mailbox, they may also gain access to Teams chats, SharePoint files, OneDrive documents, client correspondence and internal approvals. For legal and accounting firms, that exposure can reach deeply into client matters and financial records.
Multi-factor authentication enforcement reduces reliance on passwords alone and helps protect sensitive data from a phishing attack that captures credentials.
MFA Should Be Firm-Wide
MFA should apply to:
- Partners
- Accountants
- Lawyers
- Administrators
- Support staff
- Contractors
- Temporary users
- Privileged accounts
It should not be limited to senior people.
A junior user may still have access to sensitive files, shared mailboxes, client folders or internal systems. Every account deserves proper protection.
Privileged Accounts Need Stricter Controls
Administrative accounts should be treated separately from everyday accounts.
Better practice includes:
- Separate admin accounts
- No email use from admin accounts
- Stronger authentication for privileged roles
- Limited standing access
- Regular role reviews
- Alerts for privileged activity
- Removal of unused admin permissions
If one password can expose client data, the environment has not been properly hardened.
Legacy Authentication Should Be Removed
Legacy authentication methods do not support modern access controls in the same way as current authentication methods. Where legacy authentication remains available, it can undermine stronger identity protection.
Firms should review whether old protocols are still enabled and remove them where they are no longer required.
For firms looking beyond prevention and into active monitoring,Why MDR Is Essential for Cybersecurity in 2025 explains how managed detection and response supports continuous monitoring and response capability.
Data Loss Prevention for Privileged and Confidential Communications
Data loss prevention helps detect and control sensitive information as it moves through Microsoft 365.
For a professional services firm, DLP should be designed around the data the firm actually handles. Generic policies can miss important content or create unnecessary blocks. Good policies are specific, tested and tuned.
ASD’s Blueprint update highlights Microsoft Purview guidance covering sensitivity labels and data loss prevention policies, along with related controls for labelling, encryption, leakage prevention and investigation response.
What DLP Can Help Protect
DLP policies can support controls around:
- Tax file numbers
- Bank account details
- Payroll records
- Identity documents
- Client financial statements
- Contracts
- Legal correspondence
- Matter files
- Board papers
- Privileged communications
The aim is to reduce the chance of accidental or inappropriate sharing.
That may include warning a user before sending sensitive information externally, blocking certain data from leaving the firm, or applying extra controls when documents contain specific information types.
DLP Needs Context
A law firm may need to share sensitive documents with counsel, clients or regulators. An accounting firm may need to send tax or payroll information to authorised parties.
DLP should support those workflows with clear rules.
Useful controls can include:
- Sensitivity labels
- Policy tips for users
- Alerts for security teams
- Restrictions on external sharing
- Exceptions for approved recipients
- Encryption for sensitive content
- Monitoring of repeated policy matches
- Review of user behaviour where repeated matches indicate training or process gaps
DLP Does Not Replace Judgement
DLP is a control layer. It does not replace staff training, matter discipline, file naming, access reviews or clear policies.
For privileged and confidential communications, people still need to understand what they are handling and why it matters.
Azure Security: Protecting the Foundation Beneath Microsoft 365
Azure security matters because Microsoft 365 does not sit in isolation.
Identity, permissions, administration, cloud workloads, backups, app registrations, cloud services and integrations may all rely on Microsoft cloud services. If the foundation is weak, the firm’s broader Microsoft environment is weaker.
Where Azure Security Supports M365 Security
Azure security can affect:
- Identity and access management
- Administrator permissions
- Cloud applications
- App registrations
- Resource access
- Logging and monitoring
- Backup and recovery
- Security alerting
- Hybrid connectivity
For legal and accounting firms, the priority is control. The firm needs to know who can change settings, grant permissions, approve integrations, access cloud resources and manage recovery options.
Why Governance Matters
Azure environments can become messy when multiple people have administrator access, old permissions stay active, or project-based changes are never reviewed.
Legal and accounting firms should keep administration deliberate and documented.
That means:
- Limited privileged access
- Regular access reviews
- Secure change processes
- Evidence of configuration decisions
- Monitoring for unauthorised changes
Secure-by-design cloud environments are built through architecture, policy and review. They are not created by leaving the default settings untouched.
Where Azure, hybrid cloud and Microsoft 365 need to be aligned properly,Cloud Migration Services support controlled migration, Microsoft 365 optimisation, identity planning, backup and disaster recovery.
eDiscovery Readiness, Retention, and Auditability
eDiscovery readiness means the firm can locate, preserve, review and export relevant information when required.
That matters before a dispute, investigation, audit, regulator request or internal review begins. Waiting until a deadline arrives leaves the firm exposed at the exact moment it needs control.
Microsoft Purview eDiscovery can be used to identify, hold and export relevant Microsoft 365 content across services such as Exchange Online, Teams, OneDrive and SharePoint.
What Firms Need to Consider
A practical eDiscovery and retention model should consider:
- Exchange Online mailboxes
- Teams chats and channel messages
- SharePoint sites
- OneDrive accounts
- Microsoft 365 Groups
- Audit logs
- Legal holds
The goal is to make records manageable and defensible.
Auditability Matters
Audit logs help the firm understand what happened inside the environment.
They may show sign-ins, access attempts, file activity, administrative changes and sharing activity. That information can be important during internal reviews, client queries, security investigations and compliance work.
Firms that need ongoing support across Microsoft 365 administration, patching, backup and device management can also review SIAX’s Managed IT Services Melbourne offering.
Legal Professional Privilege Compliance and Practice-Ready Governance
Legal professional privilege compliance depends on confidentiality, controlled access and disciplined handling of privileged material.
Technology can support that work. It cannot carry the whole obligation.
The Law Council’s guidance on CLP and federal regulators addresses situations involving privileged communications and confidentiality duties, particularly where information or documents may be exempt from production obligations.
Accounting Firms Have Similar Confidentiality Demands
Accounting firms may not deal with legal professional privilege in the same way as law firms, yet they still handle confidential client information.
That includes tax records, payroll details, financial statements, personal information, commercial forecasts and advisory documents.
The same governance principles apply:
- Only authorised people should access sensitive files
- External sharing should be controlled
- Records should be retained appropriately
- Staff should understand handling requirements
- Access should be reviewed when roles change
- Privileged administrative access should be limited
Governance Completes the Configuration
Technology settings need documented rules behind them.
A practice-ready governance model should include:
- Defined data categories
- Approved sharing processes
- Access review schedules
- Joiner, mover and leaver controls
- Admin role approval
- Retention rules
- Response procedures
- User training
- Control ownership responsibilities
- Periodic configuration reviews
Good governance makes security repeatable. It also helps partners and compliance leaders see that the firm’s Microsoft environment is being managed with care.
For firms that need a structured way to manage controls, policies, assessments and audit evidence,Governance, Risk and Compliance services are built around practical control and defensible decision-making.
Make Microsoft 365 and Azure Fit for the Firm You Actually Run
Microsoft 365 and Azure can provide a strong foundation for legal and accounting firms. The foundation still needs to be configured for the way the firm handles confidential client data.
The M365 default security gap is the real issue. Firms often have access to strong controls, yet those controls may be incomplete, inconsistent or poorly governed.
A practice-ready environment brings together conditional access policies, multi-factor authentication enforcement, data loss prevention, Azure security, eDiscovery readiness, legal professional privilege compliance and regular governance review.
At SIAX Computing Solutions, we believe security should be built in from the start. No shortcuts. No assumptions. Just a clear, practical path to a stronger Microsoft environment. If your firm needs a clearer view of its current Microsoft 365 and Azure posture, SIAX’sCyber Security Services can help assess, strengthen and monitor the controls you need to get right.
Frequently Asked Questions
What are the key M365 security features for legal firms?
Key M365 security features include conditional access policies, multi-factor authentication enforcement, data loss prevention, sensitivity labels, audit logging, retention policies and eDiscovery readiness. Legal firms should also review external sharing, Teams access, SharePoint permissions and privileged administrator roles.
