Outlook Mailbox Cleanup Guide 

Frequently Asked Questions

1. How can I see what is using the most space in Outlook?

You can view your mailbox size using the Mailbox Cleanup tool.
Steps:
  1. Open Outlook.
  2. Select File.
  3. Select Info.
  4. Select Tools.
  5. Select Mailbox Cleanup.
  6. Select View Mailbox Size.
You will see your total mailbox size and each folder’s size.

2. How do I find and delete large emails?

Large emails take up the most space. You can search for them.
Steps:
  1. Go to the Search bar in Outlook.
  2. Type the text: size:>10MB.
  3. If needed, type: size:>5MB.
  4. Sort results by Size.
  5. Delete emails you do not need.
  6. Empty the Deleted Items folder.
  7. Select Folder and then select Recover Deleted Items to remove items permanently.

3. How do I remove attachments but keep the email?

This keeps important messages but frees space.
Steps:
  1. Open the email.
  2. Right‑click the attachment.
  3. Select Save As and choose a folder on your computer or cloud storage.
  4. Select the attachment again.
  5. Select Remove Attachment.
  6. Save the email.

4. Which folders do people forget to clean out?

These folders often become large:
  • Deleted Items
  • Junk Email
  • Sent Items
  • Conversation History
Open each folder and delete items you no longer need.

5. How can I sort my email by size?

Sorting helps you find large items quickly.
Steps:
  1. Open your Inbox.
  2. Select the Size column to sort from largest to smallest.
  3. If you do not see the Size column, follow these steps:
    • Select View.
    • Select View Settings.
    • Select Sort.
    • Select Size.
    • Select OK.

6. How do I archive older emails?

Archiving moves older emails into a different file to free space.
Steps:
  1. Select File.
  2. Select Info.
  3. Select Tools.
  4. Select Clean Up Old Items.
  5. Choose a date.
  6. Save the archive file to your computer.

7. What does “Compact Now” do?

Compacting reduces the size of your Outlook data file after you delete items.
Steps:
  1. Select File.
  2. Select Account Settings.
  3. Select Account Settings again.
  4. Select the Data Files tab.
  5. Select your data file.
  6. Select Settings.
  7. Select Compact Now.

8. How do I clean up long email conversations?

You can remove duplicate messages in a conversation thread.
Steps:
  1. Select the Home tab.
  2. Select Clean Up.
  3. Select Clean Up Folder.

9. What if my Microsoft 365 mailbox is still full?

You may have an Online Archive mailbox.
Steps:
  1. Select File.
  2. Select Info.
  3. Look for Online Archive under your mailbox information.
If available, move older emails into the Online Archive.