Use the /manage-account slash command and click on the Globally ignore account button to disable indexing of their account in the server.
This is a destructive action, equivalent to deleting your account. It will: - Remove all stored messages of your account - Not index future messages of your account - Not track analytics events of your account

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Restoring account

If you want to restore your account, use the /manage-account slash command and click on the Stop ignoring account to restore functionality.