Copilot retention decides how long your prompts stay in Microsoft 365

In the tenants I work with, compliance questions about Copilot for Microsoft 365 tend to surface earlier than people expect, often before a pilot has even started. Copilot retention usually comes up the moment the works council or the security team asks where user prompts and Copilot's answers end up, who can read them and how long they stay around. Many people assume Copilot interactions are short-lived. They aren't. Each prompt and each answer leaves traces in several places in Microsoft 365, and that has real consequences for compliance, transparency and how much users trust the tool.

Copilot stores every interaction in the mailbox and the audit log

The common assumption is that AI prompts simply vanish. What actually happens is that every Copilot prompt and the answer it produces get saved in the user's Exchange Online mailbox, in a hidden folder that normal Outlook users never see. On top of that, Copilot activity is logged in the unified audit log under its own record type (CopilotInteraction). That matters in practice: in the Purview portal you can search for Copilot interactions by filtering on the activity or record type, though KQL queries won't do it. So if you ever have to find out who asked what and when, the data exists. That helps with incident response, and just as much with governance or internal investigations.

The diagram below shows what a typical Copilot interaction looks like from a compliance point of view:

flowchart TD
  A["User submits Copilot prompt"] --> B["Copilot generates response"]
  A --> C["Prompt & response in hidden mailbox folder"]
  B --> C
  A --> D["CopilotInteraction record in audit log"]

Figure: How Copilot interactions flow into the mailbox and the audit log

Copilot retention follows the policies you set for Exchange mailboxes

For compliance, the part that really counts is the retention period. Copilot as a service doesn't keep chats or prompts itself. Instead, prompts and responses are stored as message objects in the user's Exchange Online mailbox, so your mailbox retention policies apply to them. If you delete mailbox content after 2 or 5 years, Copilot interactions go with it. If you want different rules, you can create dedicated retention settings for the hidden folder (named "Teams Chats & Copilot Interactions"), for example to remove Copilot history earlier or to keep it longer for certain roles. Departments that handle trade secrets or highly confidential matters often need exactly that.

One detail people tend to miss: the audit log has its own, limited lifetime, which depends on your licensing (90 days by default, up to one year with Purview Audit (Premium)). If you want full forensic traceability, you have to plan for mailbox retention and the audit log window together. The technical details are in Microsoft's documentation on Copilot and audit.

Only specific Purview roles can search Copilot data

Access is locked down. Copilot entries in the audit log are visible only to people with the right Purview roles, such as Compliance Administrator or Audit Reader. Searching mailboxes or running eDiscovery for prompts and responses requires dedicated eDiscovery or compliance permissions on top of that. In my experience it pays to keep privacy officers and the works council in the loop about these controls. I tell clients to be completely open about who can look at Copilot history and why. It builds trust and saves you arguments later.

Practical tip: What has worked well for me is a short FAQ or info sheet, written together with IT compliance and the works council, that explains how Copilot prompts and responses are stored and who can review them. Copilot pilots run much more smoothly with that in place.

Copilot data can be deleted, but users can't do it on their own

Sooner or later someone asks about the "right to be forgotten" in the context of Copilot. Basically, Copilot interactions behave like any other Exchange message and can be removed automatically by retention policies. Users can clear their local Copilot history in the Copilot panel in Outlook, Word, Excel or Teams, but that only affects the local history. The mailbox copy and the audit log entries stay where they are. The final say always rests with the Purview retention settings. Removing individual Copilot messages from a mailbox is technically possible with eDiscovery deletion or a script. You'll rarely need it, and it should only happen carefully and after legal review.

When I set up a targeted retention policy for Copilot interactions, I usually do it like this:

• In the Microsoft Purview compliance portal → Data lifecycle → Retention policies, create a new policy for Exchange mailboxes.
• Select the "Teams Chats & Copilot Interactions" folder explicitly as the location.
• Set the retention and deletion behaviour you want.

For more on AI scenarios in Purview, see Microsoft's documentation.

Copilot is not a compliance black box in my experience

In my daily work, Copilot for Microsoft 365 has proven a lot more transparent than many people assume. Being able to retain and audit prompts and responses isn't only a risk. It also gives you a chance to set clear expectations and bring sceptics on board. If you deal with Copilot retention early and manage it through Purview, you won't get caught out, and users and internal stakeholders will trust the rollout more. My advice is to start early, test how it behaves in your tenant and write down your approach together with the privacy and compliance teams. That effort pays for itself.