SharePoint Online Threshold Limits – Critical Impact and Architectural Guidance Request

Dear Microsoft Support Team,

We are the central IT service provider managing a productive SharePoint Online environment for one of our enterprise customers. As part of a migration project (merger), we encountered a significant issue related to the exceeding of Microsoft-recommended thresholds in SharePoint Online. The resulting impact disrupted critical business operations.

We kindly request confirmation, technical explanation, and the most up-to-date Microsoft recommendations (including sources) regarding the following topics:

Threshold Clarification

What are the current Microsoft-recommended maximum limits for:

Total number of files/folders in a document library

Total number of files/folders within a single folder or path

Maximum number of items to maintain functional permission management

Maximum number of items that allow stable OneDrive synchronization

Technical Impact Questions

What are the consequences when the 100,000-item threshold is exceeded within a folder path, especially when changing access paths (e.g., department name changes)?

What are the technical causes of the extended "re-synchronization" process triggered by path changes?

Architectural Guidance

How should a Site Collection or library be structured to ensure:

Scalability for enterprise use

Effective permission control even with over 1 million files

Smooth OneDrive sync functionality

Future-proofing against disruptive changes (e.g., metadata updates, path modifications)

Known Thresholds / Internal Guidelines:

Maximum per library: 30 million items (Source: Microsoft Docs)

Permission management limit: 100,000 items (breaking inheritance not possible beyond this)

OneDrive sync limit: 300,000 items (Source: Microsoft Docs)

Help is needed:

Recommendations on how to architect large-scale document libraries

Best practices to avoid the aforementioned issues

Clear indication of the thresholds that must not be exceeded in an enterprise-grade SPO environment