Sharing
Sharing sets how content in SharePoint Online and OneDrive can leave the tenant by default: who a link can reach, how long it lasts, and what happens to a file Defender for Office 365 flags as unsafe. The fifth baseline, Storage Warning, is an early-warning threshold for site storage rather than a sharing control; it’s in this category because it sits on the same SharePoint tenant settings.
Why it matters
SharePoint and OneDrive’s default sharing level matters because it’s set once, tenant-wide, and then forgotten: every new site inherits it unless someone deliberately tightens it. At Microsoft’s most permissive default, anyone with a link can open a file without signing in, through an anonymous link that keeps working indefinitely and traces back to no one. For an MSP, loosening this by accident is usually the fastest way to turn “we share files with clients” into “anyone who finds the link can read them”.
How Microsoft evaluates it
External sharing is a single tenant-level SharePoint Online policy, found under Policies → Sharing in the SharePoint admin centre. It has one setting for SharePoint and a separate one for OneDrive that can be set more restrictively, ranging from Anyone at the most permissive end to no external sharing at all. On top of that, this category’s baselines tune the default link type and permission offered, whether guests can reshare what’s been shared with them, and how long an anonymous link keeps working before it expires. Whatever level a site is set to, the more restrictive of the site’s and the tenant’s settings always wins. Blocking infected-file downloads is a separate Defender for Office 365 check, run at download time rather than share time. (Microsoft Learn: Manage sharing settings for SharePoint and OneDrive in Microsoft 365, Overview of external sharing in SharePoint and OneDrive)
What end users experience
Tightening the sharing level changes what users are offered when they share a file: the default link becomes the narrowest option (specific people, view-only) instead of the widest, and external sharing may need the recipient to already be a guest in the tenant’s directory rather than accepting anyone with the link. Anonymous links already out there stop working once they reach the expiry window, without any notice to whoever sent them. A file Defender for Office 365 finds infected can’t be downloaded; the user sees a block instead of the file. Storage Warning is aimed at admins rather than end users, and nothing appears until a site approaches the threshold set.
| Baseline | Scope | Licence |
|---|---|---|
| Anonymous Links Expiry | Tenant | SharePoint Online |
| External (Guest) Users Resharing | Tenant | SharePoint Online |
| Global Default Sharing Policy | Tenant | — |
| SharePoint Block Infected Files Download | Tenant | Defender for Office 365 |
| SharePoint Storage Warning | Tenant | SharePoint Online |