Microsoft 365 sharing is the set of tenant controls that decide how content is shared across collaboration services such as SharePoint, OneDrive, and Teams. These controls include external sharing settings, guest access, link permissions, expiration rules, and who can create or forward sharing links. In practice, they determine whether a file stays inside the organization, is shared with named users, or becomes accessible more broadly.
This matters because sharing is a common path for accidental data exposure and attacker abuse. A weak policy can leave sensitive files reachable through old links, overbroad group permissions, or unmanaged guest accounts. In real incidents, attackers may use compromised accounts to create new sharing links, export documents, or hide access through collaboration features. Defenders reduce risk by restricting external sharing, enforcing sensitivity labels and DLP, reviewing permissions, and auditing sharing events so unusual access changes are detected quickly.