Fix Teams eDiscovery Search Misses Chat Messages for a Guest Conversation

When you run an eDiscovery search in Microsoft Teams, chat messages from a guest conversation may not appear in the results. This happens because guest conversations are stored in a separate content location that is not included by default in your search query. In this article, you will learn why guest chat messages are missed and how to configure your eDiscovery search to include them.

The root cause is that Teams stores guest chat messages in the guest user’s mailbox, not in the host organization’s Exchange mailboxes. Standard eDiscovery searches only target mailboxes in your organization, so guest content is skipped unless you explicitly add the guest’s mailbox as a data source. You will also learn how to verify that your search covers all relevant locations and how to avoid common pitfalls.

By the end, you will be able to run a complete eDiscovery search that captures guest conversations, and you will know how to check whether your search is actually including them.

Why Teams eDiscovery Misses Guest Chat Messages

Teams stores chat messages in the mailbox of each participant. For internal users, that mailbox is your organization’s Exchange Online. For guest users, the mailbox belongs to the guest’s home tenant, which is outside your organization. When you run an eDiscovery search, you normally search only the mailboxes in your tenant. Guest mailboxes are not part of that default set.

The guest’s chat messages are stored in the guest’s own mailbox, but those messages are also copied to the host tenant for compliance purposes. That copy is what you need to find. However, eDiscovery does not automatically know about that copy unless you add the guest’s mailbox as a data source.

How Guest Chat Storage Works

When a guest joins a Teams conversation, the chat history is saved in the guest’s mailbox in their home tenant. At the same time, a copy is placed in the guest’s mailbox in your tenant, which is a special mailbox that holds only the guest’s Teams content. This copy exists so your organization can meet compliance requirements without needing access to the guest’s home tenant.

Your eDiscovery search must include that guest mailbox explicitly. If you search all mailboxes, the guest mailbox is not included because it is not a standard user mailbox. You must add it manually by entering the guest’s email address.

Steps to Include Guest Chat Messages in an eDiscovery Search

The steps below show how to create a new eDiscovery search that includes guest chat messages. You will use the Microsoft Purview portal.

1. Open the Microsoft Purview portal
   Go to https://compliance.microsoft.com and sign in with an account that has eDiscovery Manager permissions.
2. Navigate to eDiscovery
   In the left navigation, select eDiscovery and then choose New search.
3. Name your search
   Enter a descriptive name like “Guest chat review” and click Next.
4. Choose locations
   Under Locations, select Specific mailboxes. Type the guest user’s full email address and click Add. Repeat for any other guests you need to include.
5. Add search conditions
   Under Query builder, click Add condition. Select Participants and enter the guest’s email address. This ensures the search captures messages where the guest is a participant.
6. Run the search
   Click Search and wait for the results. Review the count to confirm that guest messages appear.
7. Export the results
   Once the search completes, click Export and choose the output format you need.

Verify That the Guest Mailbox Is Included

After you run the search, check the search summary. It shows the number of items found and the locations that were searched. If the guest mailbox is not listed, go back and add it again. You can also use the preview function to see whether guest chat messages appear in the results.

If eDiscovery Still Misses Guest Chat Messages After Adding the Mailbox

Sometimes adding the guest mailbox is not enough. The following issues can cause guest chat messages to remain missing.

Guest Chat Messages Are Missing Because the Guest Was Removed from the Tenant

If the guest user was removed from your tenant, their mailbox copy is deleted. You cannot recover that content through eDiscovery. To avoid this, keep guest accounts active while you need to search their data. If you must remove a guest, export their data first.

Guest Chat Messages Are Missing Because the Search Only Covers Chat Type

Teams eDiscovery can search chats, channels, and meeting content. If your search query does not include the Chat type, guest chat messages will not appear. In the search query, add kind:chat to ensure you capture chat messages specifically.

Guest Chat Messages Are Missing Because of a Policy Hold

If your organization applies a retention policy that deletes guest chat content after a short period, older messages may no longer exist. Check your retention policies to confirm that guest chat data is kept long enough for your eDiscovery needs.

Teams eDiscovery Search with Guest Mailbox vs Default Search

Item	Default Search (All Mailboxes)	Search with Guest Mailbox Added
Scope	Only internal user mailboxes	Internal mailboxes plus guest mailboxes
Guest chat messages	Not included	Included
Setup effort	None	Manual addition of guest email addresses
Compliance coverage	Incomplete for guest conversations	Complete for guest conversations

Conclusion

You can now run an eDiscovery search that includes guest chat messages by adding the guest’s mailbox as a data source. Make sure to add the guest mailbox explicitly and use the Participants condition to filter for the guest. To verify your search works, check the search summary to confirm the guest mailbox is listed. Remember to keep guest accounts active and review retention policies so you do not lose data. For advanced cases, consider using the eDiscovery export function to save results for legal review.