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Quick Answer

Select an email thread, go to the Home tab, and click Clean Up > Clean Up Conversation to delete redundant messages.

How to Clean Up Email Conversations in Outlook ​

Applies to: Microsoft 365 (Outlook desktop)
Article Type: How-To
Last Updated: 2026-03-09

Summary ​

Long email threads create duplicate content in your mailbox — every reply includes the full history of previous messages. Outlook's Conversation Clean Up feature removes these redundant copies, freeing up space and keeping your folders tidy.

Conversation Clean Up is not the same thing as Conversation view. Clean Up deletes messages; the view setting only groups them on screen. If your problem is that replies are stacked into threads and you want them listed separately, you want How to Turn Conversation View On or Off in Outlook instead — no mail is deleted there.

Prerequisites ​

  • Microsoft Outlook desktop (Classic). Conversation Clean Up is not available in New Outlook or the Web.

Instructions ​

1. Clean Up a Single Conversation ​

Remove redundant messages from one email thread.

  1. Select any message in the conversation you want to clean up.
  2. Go to the Home tab.
  3. Click Clean Up > Clean Up Conversation.
  4. A confirmation dialog appears — click Clean Up.
  5. Outlook moves redundant messages (those whose content is fully contained in a later reply) to Deleted Items.

2. Clean Up an Entire Folder ​

Remove redundant messages from all conversations in a folder at once.

  1. Select the folder you want to clean up (e.g., Inbox).
  2. Go to the Home tab.
  3. Click Clean Up > Clean Up Folder.
  4. Click Clean Up Folder in the confirmation dialog.
  5. Outlook processes every conversation in that folder and moves redundant messages to Deleted Items.

3. Clean Up a Folder and Subfolders ​

Apply cleanup recursively to a folder and everything inside it.

  1. Select the parent folder.
  2. Click Clean Up > Clean Up Folder & Subfolders.
  3. Click Clean Up Folder in the confirmation dialog.

4. Configure Clean Up Settings ​

Customize which messages are kept or removed.

  1. Go to File > Options > Mail.
  2. Scroll down to the Conversation Clean Up section.
  3. Adjust settings:
    • Cleaned-up items destination: Choose a folder other than Deleted Items if preferred.
    • Don't move unread messages — keeps unread replies even if redundant.
    • Don't move categorized messages — preserves color-coded emails.
    • Don't move flagged messages — preserves follow-up items.
    • Don't move digitally-signed messages — preserves signed emails.
  4. Click OK to save.

Troubleshooting ​

TIP

Run Conversation Clean Up on your Inbox monthly to keep mailbox size under control. Pair this with the Outlook mailbox size check to stay well below the 50 GB limit.

Symptom / ErrorPotential CauseSolution
No messages were cleaned upThread has only one messageClean Up only removes messages whose content is fully duplicated in a later reply. Single-message threads are not affected.
Important email was moved to Deleted ItemsMessage was redundant by contentRecover it from Deleted Items. Adjust the Clean Up settings to exclude flagged, categorized, or unread messages.
Clean Up option is greyed outNo conversation selectedSelect an email within a conversation thread before clicking Clean Up.