Unlike standard Exchange email records, Microsoft Teams data does not sit in a single repository. Chat strings, group channel files, and wiki edits are scattered across Exchange mailboxes, SharePoint structures, and OneDrive folders. If your company faces regulatory frameworks (such as GDPR, HIPAA, or FINRA), leaving your messaging history unmanaged poses a massive liability risk. This step-by-step handbook walks through setting up custom Retention Policies to automatically delete or retain messages, alongside initiating formal eDiscovery Cases to legally lock down evidence.

Stage 1: Architecting Microsoft Teams Data Layouts

Before writing preservation policies, you must understand exactly where the system routes user conversations under the hood. While chats appear seamlessly inside the client app, the storage architecture is completely split:

• 1:1 & Group Chats: Stored within a hidden, system-protected folder inside each individual participant’s personal **Exchange Online Mailbox**.
• Standard Channel Messages: Saved within a hidden sub-folder located in the specific **Group Mailbox** attached to that team.
• Shared & Private Channel Messages: Channeled directly into specialized **System Mailboxes** dedicated to that channel’s explicit membership group.

Stage 2: Building Targeted Retention Policies

Retention policies allow you to choose whether to keep data for legal protection or delete old messages to lower data risks.

Step 2.1: Initializing the Retention Rule Wizard

1. Log into the Microsoft Purview Compliance Portal using Data Protection or Global Admin rights.
2. In the left-side panel navigation index, open Data Lifecycle Management > Microsoft 365, then click Retention Policies.
3. Select the New retention policy action button to trigger the setup wizard.

Step 2.2: Isolating Teams Messaging Environments

On the **Locations** step, turn off all default standard sliders (like Exchange mail and SharePoint sites) and focus your policy solely on chat endpoints.

Step 2.3: Enforcing Timelines and Cleanup Action Triggers

Define whether your primary goal is preservation or compliance cleanup:

• For Defensible Deletion: Set the policy to Only delete items when they reach a certain age (e.g., Delete all chat entries exactly 30 days from creation date to reduce organizational liability).
• For Strict Retention: Set the policy to Retain items for a specific period, then choose Do nothing or Delete items automatically once that timeframe runs out.

Stage 3: Running eDiscovery Searches & Placing Litigation Holds

When an internal investigation or external legal notice lands, you need to quickly locate and lock relevant conversations to prevent users from altering or erasing evidence.

Step 3.1: Provisioning a New eDiscovery Case

1. Inside the Microsoft Purview portal, expand eDiscovery and select Standard (or Premium based on licensing).
2. Click Create a case, input a unique internal case name and tracker ID number, and save.
3. Open the newly created case file and navigate directly to the Hold tab panel area.

Step 3.2: Applying an Immutable Litigation Hold

Click Create under the Hold layout banner. Select the target user mailboxes or complete team groups involved in the legal matter. Once applied, even if a user edits or deletes a chat message on their desktop app, the system safely saves the original copy within the secure, hidden Exchange data folder for audit review.

Step 3.3: Extracting and Exporting Audited Conversations

Once your content queries wrap up, choose Export results from the Actions dropdown list. Select your preferred layout format: you can export chats as individual email messages or group them into a single, structured PST file that maps out conversational threads chronologically.