How to Find and Delete Large Older Emails in Microsoft 365 Outlook

Goal

Your mailbox is near or over its storage limit. The goal is to find older emails with large attachments and delete messages that are no longer needed so the mailbox can get below the 50GB or 100 GB limit.

A good starting point is to search for emails that are:

  • Older than 2 years
  • Have attachments
  • Are larger than 5 MB
Important Before You Start

Only delete emails you are sure you no longer need.

Do not delete messages that may be needed for legal, accounting, HR, customer records, or business history.

If an attachment is important but the email does not need to stay in your mailbox, save the attachment first to OneDrive, SharePoint, your company file server, or another approved storage location.

Do not use the normal Outlook “Archive” button for this cleanup unless instructed by IT. In many cases, the Archive button only moves the email to another folder inside the same mailbox, which does not reduce mailbox size.

Step 1 — Open Outlook on the Web

  1. Open a web browser.
  2. Go to Outlook on the web.
  3. Sign in with your Microsoft 365 email account.
  4. Make sure you are in Mail.

Step 2 — Choose the Date for “Older Than 2 Years”

You need to search for emails received before a specific date.

Example:

If today is June 26, 2026, then “older than 2 years” means emails received before June 26, 2024.

The date should be entered in this format:
MM/DD/YYYY

Example:
06/26/2024

Step 3 — Search for Large Older Emails With Attachments

At the top of Outlook, click in the Search box.

Enter this search:
received:<06/26/2024 hasattachment:yes messagesize:>5 MB

Then press Enter.
Replace 06/26/2024 with the date that is two years before today.

This search is looking for emails that:

  • Were received before the date entered
  • Have attachments
  • Are larger than 5 MB

Step 4 — Search All Folders, Not Just Inbox

After the search results appear, make sure the search is checking the entire mailbox, not only the Inbox.

Look for the folder filter near the search results.

Choose one of these options if available:

  • All folders
  • Current mailbox
  • All mailboxes
The exact wording may vary depending on your Outlook version.

Step 5 — Review the Search Results Carefully

Do not select everything and delete it blindly.

Open messages if you are unsure what they contain.

Good candidates for deletion usually include:

  • Old newsletters
  • Old reports that are no longer needed
  • Duplicate attachments
  • Old scans
  • Old photos
  • Old vendor quotes
  • Old email chains with large attachments
  • Sent messages with large files attached
Be extra careful with:

  • Contracts
  • Tax records
  • Legal emails
  • HR emails
  • Customer records
  • Project documentation
  • Anything related to compliance or audits

Step 6 — Save Attachments You Need to Keep

If you need to keep an attachment but not the email:

  1. Open the email.
  2. Download or save the attachment.
  3. Store it in the correct approved location, such as OneDrive, SharePoint, or the company file server.
  4. After confirming the file is saved, you can delete the email if the email itself is no longer needed.

Step 7 — Delete Emails in Small Batches

It is safer to delete in smaller groups instead of deleting hundreds or thousands of emails at once.

Recommended batch size:

  • 25 to 50 emails at a time
To delete:

  1. Check the box next to each email you want to remove.
  2. Click Delete.
  3. Continue reviewing and deleting additional batches.

Step 8 — Repeat the Search in Sent Items

Large attachments are often found in Sent Items because those are files you sent to other people.

Run the same search again, but filter the results to Sent Items if Outlook gives you a folder filter.

Search:

received:<06/26/2024 hasattachment:yes messagesize:>5 MB

Then filter to:

Sent Items

Delete old sent emails with large attachments that are no longer needed.


Step 9 — Try a Broader Search If Needed

If the mailbox is still too large, repeat the same process with a larger date range or larger search.

Option 1 — Find all emails older than 2 years with attachments:

received:<06/26/2024 hasattachment:yes

Option 2 — Find very large emails regardless of date:

hasattachment:yes messagesize:>10 MB

Option 3 — Find emails larger than 20 MB:

hasattachment:yes messagesize:>20 MB

Start with the largest and oldest items first.


Step 10 — Empty Deleted Items

Deleting email moves it to Deleted Items first. It may still count against the mailbox size until Deleted Items is emptied.

After you are sure you no longer need the deleted messages:

  1. Go to the Deleted Items folder.
  2. Right-click Deleted Items.
  3. Choose Empty Folder.
Or:
  1. Open Deleted Items.
  2. Click Empty folder if that option appears.
Only empty Deleted Items after you are sure the deleted messages are no longer needed.

Step 11 — Empty Junk Email

Junk Email can also use mailbox space.

  1. Open the Junk Email folder.
  2. Review anything that might be legitimate.
  3. Delete or empty the folder if nothing needs to be kept.

Step 12 — Wait for Mailbox Size to Update

After deleting and emptying Deleted Items, the mailbox size may not update immediately.

It can take some time for Microsoft 365 to recalculate the mailbox size.

If the mailbox still shows as full right away, wait and check again later.

Recommended Cleanup Order

Start with this order:

  1. Sent Items older than 2 years with attachments larger than 5 MB
  2. Inbox older than 2 years with attachments larger than 5 MB
  3. Other folders older than 2 years with attachments larger than 5 MB
  4. Emails larger than 10 MB
  5. Emails larger than 20 MB
  6. Deleted Items
  7. Junk Email
This approach usually removes the largest unnecessary items first while reducing the chance of deleting important current email.