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The Mail app on macOS is one of the biggest hidden storage consumers. Whether you’re using an older macOS version (Catalina, Big Sur, Monterey, Ventura) or newer ones like macOS Sonoma 14, Sequoia 15, or Tahoe 26, Mail can silently accumulate tens of gigabytes of attachments, cached messages, and system files.

If you notice your Mac running out of storage unexpectedly, Mail is often the culprit.

This guide explains every safe method to free up space—from beginner-friendly steps to advanced cleanup options.

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1. Check How Much Storage Mail Is Using

Before clearing anything, confirm the Mail app is the problem.

On macOS Ventura, Sonoma, Sequoia, and Tahoe

1. Click Apple Menu () > System Settings
2. Go to General > Storage
3. Look for Mail in the list
4. Check how many GB it uses

On Older macOS Versions

1. Click the Apple Menu > About This Mac
2. Select Storage > Manage…
3. Select Mail

If Mail is using multiple gigabytes, continue to the steps below.

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2. Delete Mail Attachments (Safest and Most Effective)

Mail stores attachments locally, even if your account uses IMAP. You can delete attachments without deleting the emails themselves.

Method A: Remove Attachments from Selected Emails

1. Open Mail
2. Select any email(s)
3. In the menu bar, choose
   Message > Remove Attachments

The email remains, but the attachment files are deleted.

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3. Clear the Mail Downloads Folder (Often 5–30 GB)

Mail automatically saves every opened attachment into a hidden folder.

Steps

1. Open Finder
2. At the top, click Go > Go to Folder…
3. Enter:

~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads/

4. Delete all files in it (these are duplicates — safe to remove)

On older macOS versions, also check:

~/Library/Mail/V10/MailData/Downloads

(V10 varies by macOS version — V7, V8, V9, etc.)

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4. Clean the Mail Cache (Rebuild Indexes Safely)

Mail creates cache files for message previews, attachments, and images.

Steps to Clear Cache

1. Quit Mail completely
2. Open Finder
3. Click Go > Go to Folder…
4. Enter:

~/Library/Mail/

5. Inside this folder, only delete these safely removable items:
   • Envelope Index
   • Envelope Index-shm
   • Envelope Index-wal
6. Then reopen Mail; it will rebuild the index.
   This can reduce storage significantly.

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5. Empty the Junk and Trash Mailboxes

These folders often accumulate thousands of messages.

How to do it

1. Open Mail
2. Right-click Trash → Erase Deleted Items
3. Right-click Junk → Erase Junk Mail

This alone can free several GB depending on your usage.

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6. Use macOS “Optimize Storage” Tools

Modern macOS versions include built-in tools to automatically manage storage.

Enable the feature

1. Go to System Settings > General > Storage
2. Enable:
   Optimize Storage for Mail

This removes locally stored attachments and keeps them in iCloud or your mail server.

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7. Remove Old Email Accounts You No Longer Use

If an old account is still configured in Mail, macOS continues to sync and store all its content.

Remove an unused account

1. Open Settings > Internet Accounts
2. Select the account
3. Click Delete Account

This deletes all associated mail and attachments from your Mac (emails remain on the server if IMAP).

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8. Rebuild Mailboxes for Better Performance & Lower Storage

If Mail behaves slowly or stores unnecessary cached content:

Steps

1. Select a mailbox
2. From the Menu bar choose:
   Mailbox > Rebuild

This forces macOS to re-download only necessary emails and discard corrupted or cached files.

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9. Reset Mail Storage Completely (Advanced Users)

If your Mail folder is excessively large (20–50 GB), a full reset might help.

Steps

⚠️ This does not delete emails on IMAP/Exchange — only local Mac data.

1. Quit Mail
2. Open Finder > Go to Folder…
3. Enter:

~/Library/Mail/

4. Move the entire Mail folder to the Desktop (backup)
5. Reopen Mail → It will rebuild from the server
   (This may take time depending on inbox size)

After confirming everything syncs correctly, delete the backup folder.

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10. Additional Tricks to Reduce Mail Size Quickly

A. Remove Large Attachments Using Search

1. In Mail, click the Search bar
2. Type attachment
3. In the sidebar, choose Contains Attachments or Message has Attachments
4. Sort by size and delete unnecessary emails

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B. Convert Old Accounts From POP to IMAP

POP emails stay stored forever on your Mac.
IMAP stores emails on the server, reducing local usage.

If possible, migrate to IMAP.

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Finally

Mail storage is one of the biggest hidden space consumers on macOS — especially on older Macs with limited SSD sizes.

By following the steps in this guide, you can easily free 5–30 GB or more depending on your email usage.

Whether you’re using an older macOS or the latest macOS Sequoia/Tahoe, these methods work safely and effectively.