SharePoint migration doesn’t end when content is moved to the new environment. In many organizations, it’s actually the point where security risk begins to build. Permissions can expand, external sharing may become harder to monitor, and the governance controls established during migration often weaken over time.
Post-migration security requires a governance plan to keep your data secure. Without governance, SharePoint environments retain legacy access models, overshared content and inconsistent controls that no longer align with current operational or compliance requirements. These conditions introduce exposure that often goes undetected until an incident occurs.
This article covers the five essential security controls to deploy immediately after migration, from permission cleanup to Microsoft Purview automation.
1. Permission Management and Access Control
Migration tools move files and folders but do not clean up the permission sprawl that gets accumulated over years. This means inherited permissions get broken, individual user access gets hardcoded and exceptions pile up without documentation.
Post-migration is your opportunity to simplify before users start creating new sites and replicating old patterns. Focus on four areas: restoring inheritance, moving to group-based access, removing unique permissions, and enforcing least privilege.
Simplify Permission Inheritance
Every time permission inheritance is broken, complexity creeps in. During migrations, this often happens automatically and without a clear reason.
Start by auditing areas where permissions were customized years ago. When inheritance is restored, everything becomes clearer. Outdated custom permissions disappear, access rules make sense again and managing SharePoint feels far less painful. Fewer exceptions also mean fewer security gaps.
Implement Group-Based Access
Assigning permissions directly to individual users works until it becomes unmanageable. People move roles, teams expand, and access quietly stops reflecting how work actually gets done.
Group-based access solves this by tying permissions to roles instead of individuals. When someone changes teams, you update group membership in one place rather than hunting down scattered individual permissions across sites.
Reviews become quicker, errors are easier to catch and access stays aligned as the business shifts. Over time, this approach prevents SharePoint from turning into a platform of one-off permissions.
Audit and Remove Unique Permissions
Unique permissions are easy to miss and hard to track. While they were usually created for a reason that made sense at the time, that justification often no longer applies.
Post-migration is the right moment to surface files and folders with custom access, permissions that bypass group controls, and users who should no longer have access.
Apply Least Privilege Access
Access tends to grow over time and rarely declines, which is how sensitive data becomes visible to the wrong audience.
Least privilege introduces a clear, repeatable way to control access growth over time. It starts with read access, increases permissions only when there is a clear operational need, and requires elevated access to be reviewed regularly.
When access is intentional rather than inherited by default, SharePoint stays secure without slowing people down.
2. Information Protection with Microsoft Purview
Cleaning up permissions is just the start. Protecting the data itself is what really keeps your SharePoint environment safe. Microsoft Purview provides tools to automatically classify, retain, and safeguard your content so you don’t have to chase problems after they happen.
Post-migration is the perfect time to put these protections in place. Deploy them in sequence by classifying content with sensitivity labels, defining retention requirements, and then adding DLP policies as your final safety net.
Deploy Sensitivity Labels
Not every document needs the same level of protection. Sensitivity labels make it easy to mark content based on risk and enforce rules automatically.
Start by classifying content into clear categories like Confidential, Internal or Public. Apply encryption to sensitive documents to prevent unauthorized access, especially for files shared externally. Where possible, automate labeling to reduce user error and ensure consistency across the environment.
With sensitivity labels, security becomes less about remembering the rules and more about following a system that works for everyone.
Configure Retention Labels
Old content can linger, creating compliance headaches or increasing exposure. Retention labels help you keep what’s necessary and remove what’s not.
Set retention periods according to business or legal requirements. Use auto-apply rules for large sets of content to ensure consistent enforcement without manual intervention then ensure that deleted items remain recoverable if required for audits or regulatory compliance.
Set Up Data Loss Prevention (DLP) Policies
Even with proper permissions and labels, mistakes happen. DLP policies provide a safety net to prevent accidental leaks of sensitive information.
Begin by identifying sensitive data types like personal information, financial records or trade secrets. Create rules to block or warn users before sensitive content is shared externally. Monitor incidents regularly and adjust policies as your SharePoint environment evolves.
Related Resource – Microsoft Data Loss Prevention With Purview
3. External Sharing Governance
External sharing is one of SharePoint’s most useful but risky features. After migration, it’s easy for content to be overexposed, especially when inherited permissions are imported.
Configure External Sharing Policies
Not everyone needs to share files outside of your organization. Clear policies help you avoid accidental leaks.
Start by limiting external sharing to specific domains or trusted partners. From there, establish clear ownership over who is allowed to share content outside the organization (typically site owners or group administrators). Finally, review sharing settings at both the tenant and site levels and adjust them as needed to ensure they continue to align with your organization’s risk tolerance.
Enable “Mark New Files Sensitive by Default”
New files can slip through without protection, especially when teams collaborate quickly. Automatically marking them as sensitive helps close that gap.
Configure SharePoint and OneDrive to apply sensitivity labels by default. Educate teams on why labeling matters, but depend on automation to consistently enforce the rules. Regularly review your default settings to ensure they still align with your organization’s risk profile.
Block External Access to Labeled Content
Even with labels and permissions in place, sensitive files can still be shared externally if policies are not enforced. Blocking external access for high-risk content adds a critical layer of protection.
Apply blocking rules to highly sensitive or confidential labels and combine them with DLP policies for monitoring and user guidance. Review blocked content regularly to ensure legitimate sharing requests are handled securely.
4. Audit and Monitoring Strategy
After cleaning up permissions, labeling data and controlling external sharing, the next step is keeping an eye on everything. Post-migration is the ideal time to set up audit and monitoring processes that catch issues early and keep your SharePoint environment secure.
Enable Unified Audit Logging
Audit logs give you visibility into what’s happening across SharePoint. They’re essential for detecting anomalous activity before it escalates into a problem.
Turn on unified audit logging in Microsoft 365 to track file access, sharing and administrative activity. Ensure logs are accessible to security and compliance teams and review them regularly to identify trends or unusual patterns.
Set Up Alert Policies
Even with logs, you don’t want to wait for a monthly review to find problems. Alerts make sure you know about risky activity as it happens.
Configure alerts for external sharing, permission changes, and data access anomalies. Adjust thresholds so alerts are meaningful but not overwhelming. Make sure to combine them with DLP policies to automatically protect sensitive content when issues are detected.
Schedule Regular Permission Reviews
A one-time cleanup isn’t sufficient as permissions often change when users join, leave or move roles.
Set up quarterly or semi-annual reviews of site and library permissions to confirm that group memberships and unique permissions still reflect current roles. Remove or adjust access as your organization shifts to prevent permission sprawl from creeping back in.
5. Site Provisioning and Template Standards
Once permissions, labelling and monitoring are in place, controlling how new sites are created becomes crucial. Without standards, SharePoint can quickly become chaotic with inconsistent structures, unclear ownership, and accidental exposure.
Create Custom Site Templates
Custom templates help your teams create new sites quickly without compromising governance. Build templates with pre-configured permissions, libraries and sensitivity labels already in place. Include default navigation, metadata and compliance settings so users don’t have to think about security when creating a new site.
Update templates periodically to reflect evolving governance rules. This keeps new sites aligned with current standards without requiring constant intervention from your admin team.
Enforce Naming Conventions
Consistent naming makes content easier to find, manage, and audit. Define a clear naming convention for sites, libraries and lists that includes department, project, or function identifiers.
Automate Compliance Baselines
Automation ensures every new site meets your minimum security and compliance requirements from the start. When compliance happens automatically, users can focus on their work instead of navigating security requirements.
Automatically apply default sensitivity labels and retention policies through your site templates. Include DLP rules and external sharing restrictions so protection is built in rather than retrofitted later.
Conclusion
Post-migration is your opportunity to address what has accumulated over the years: permission sprawl, unlabeled content, uncontrolled external sharing, and inconsistent site structures. Once users settle in and start creating new sites, governance becomes harder to enforce.
Start with permissions. Simplify inheritance, move to group-based access and enforce least privilege before bad habits take root. Deploy Microsoft Purview tools to automatically classify and protect content. Lock down external sharing with clear policies and default protections. Set up monitoring so you catch issues early instead of discovering them during an audit.
We help organizations secure and govern SharePoint environments after migration by using Microsoft-native security and compliance capabilities. If you need to validate your SharePoint post-migration security posture or establish a sustainable governance framework, we can help.
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