If you receive a message titled “Your mailbox is almost full”, it means you’re near your storage limit. When your mailbox exceeds the quota, you won’t be able to send or receive new emails.

This guide helps you free up space safely using Outlook.

  1. View Folder Storage Usage
    Go to https://outlook.office.com

    Click the Settings (⚙️) icon → Account → Storage.

    You’ll see a breakdown of folders by size.

    Often, the Deleted Items and Sent Items folders consume the most space.

    In the example above, the Deleted Items folder uses 39.26 GB (80% of your mailbox), which can be cleared to recover space immediately.

  2. Empty the Deleted Items, Junk and/or Sent Items Folder
    In the Storage view, click Empty next to Deleted Items. Select All.


    Hit OK to confirm the action — this permanently removes those emails.

    Repeat for Junk Email if needed.
    💡 Tip: This usually frees the most space right away.

  3. Keep It Clean Going Forward
    a. Regularly empty Deleted Items and Junk Email.
    b. Save large attachments to OneDrive instead of keeping them in Outlook.
    c. Delete old or unnecessary emails every few months.