One-page guide / Microsoft 365

External Sharing: Who Can Access Your Data?

Harris Ejiofor, CISM – CyberShield Advisory

Sharing files with clients and partners is part of normal work, but links and guest access can quietly outlast their purpose. This guide explains what to check in Microsoft 365.

The short version

Microsoft 365 makes it easy to share a file or folder with someone outside your organization. That convenience is the point, and it is also the risk. A sharing link sent months ago may still work. A guest added for one project may still be able to open files. A link that anyone can use may have been forwarded far beyond the person it was meant for. External sharing is not a problem to eliminate. It is something to decide on purpose and review.

The main ways data travels outward

Links that anyone can open. These need no sign-in, so you cannot tell who used them.
Links for specific people. These are more controlled, but they can still last long after the work ends.
Guest accounts. An outside person is added to your environment and may keep access to teams, sites and files.
Sharing from personal storage. Staff may share work files from personal accounts you cannot see or manage.
Connected apps. Third-party apps can be given permission to read files.

Decisions worth making deliberately

Who may share externally. Everyone, or only some roles or sites that need it.
What kinds of links are allowed. Some organizations choose to limit open links and prefer links tied to named people.
How long access lasts. Links and guest access can often be given an expiry date, depending on your configuration and license.
Which sites are more sensitive. Folders with client, financial or patient information may deserve stricter rules than a general marketing folder.
Who reviews it. Someone should look at what is shared externally on a schedule.

Questions to ask this week

Can our staff share files with anyone on the internet, and do we know how often they do?
Can we list the guests who have access, and does each one still need it?
Do shared links expire, or do they last until someone removes them?
When a client engagement or project ends, who removes access?

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