If your Mac's storage is mysteriously full and you use Apple Mail, there's a good chance Mail is the culprit. Mail taking up space on Mac is a surprisingly common problem — the app caches every attachment, inline image, and downloaded file it ever touches, and those caches accumulate quietly in folders most users never open. Here's exactly where that data lives, how to measure it, and how to remove it safely without losing a single email.
Why Apple Mail Eats So Much Disk Space
Apple Mail does three things that balloon your storage:
- Caches message bodies and attachments for every IMAP account, so you can read emails offline. If you have multiple accounts, each one gets its own cache.
- Saves every attachment you open — PDFs, Word docs, Zip archives — into a hidden Mail Downloads folder, even after you've "closed" the file.
- Mirrors your entire mailbox locally if your IMAP settings prefer local storage, which can duplicate gigabytes of data already stored on the server.
The result: accounts with years of attachments routinely occupy 10–40 GB, and the storage shows up as "System Data" or "Mail" in macOS Settings, which gives you no path to actually remove it.
Where Apple Mail Stores Its Files
Before deleting anything, it helps to know exactly which folders are involved. Open Finder, press Command-Shift-G, and navigate to each path below to see the sizes yourself.
1. Mail Message Store
~/Library/Mail/V10/This is the main database folder. It contains every downloaded message body, folder structure, and embedded image for all your accounts. The version number (V10 on macOS Sonoma/Sequoia/Tahoe) may differ on older systems. Do not delete this folder manually — removing it can corrupt your mailbox index or force Mail to re-download everything from scratch in an uncontrolled way.
2. Mail Downloads Folder
~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads/Every attachment you open from Mail ends up here. This folder is the safest target: its contents are copies, not originals. The original attachment still lives on your mail server and inside the Mail message store. Deleting this folder will not remove attachments from your emails.
3. Mail Caches (inside Containers)
~/Library/Containers/com.apple.mail/Data/Library/Caches/Temporary data Mail uses for rendering and search. Safe to clear while Mail is closed; Mail rebuilds these automatically.
4. Messages and FaceTime Attachments
~/Library/Messages/Attachments/If iMessage storage is also bloated, attachments from the Messages app live here — separate from Mail but often confused with it.
How to See the Real Sizes Before You Delete
The fastest way to measure these folders from Terminal:
du -sh ~/Library/Mail/
du -sh ~/Library/Containers/com.apple.mail/
du -sh ~/Library/Messages/Attachments/Run each command and note the sizes. If you'd rather see everything in a visual map, Crumb's whole-Mac audit surfaces the com.apple.mail container in its largest-item list so you can see exactly how much each Mail folder occupies before you touch anything — useful if you want confirmation before committing to a manual delete.
How to Clear Mail Attachments and Downloads Safely
Option A — Remove Mail Downloads (Safest)
- Quit Apple Mail completely (Command-Q).
- In Finder, press Command-Shift-G and paste:
~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads - Select all files inside (Command-A), then move them to Trash.
- Empty the Trash.
- Reopen Mail — your emails and their attachments are untouched.
This is permanent. The copies in Mail Downloads are gone, but the attachments remain accessible from within each email (Mail will re-download them from the server when you open the message again, as long as the server copy exists).
Option B — Remove Attachments via Apple Mail's Built-in Tool
For attachments embedded in older emails you no longer need:
- Open Mail and select one or more messages.
- Go to Message > Remove Attachments.
- Confirm. Mail strips the attachment from the local copy of that message.
Important: This is a permanent, local operation. If the attachment no longer exists on your mail server (common with older emails or POP3 accounts), it will be gone for good. Do not use this casually on messages whose attachments you might need later.
Option C — Reduce How Much Mail Caches Locally
For IMAP accounts, you can tell Mail to cache less:
- Open Mail → Settings (Command-comma).
- Click Accounts, select an account, then open Account Information.
- Under "Keep copies of messages for offline viewing," choose Don't keep copies of any messages or Only messages I've read.
- Mail will prompt you to remove existing local copies — confirm if you want to reclaim space now.
This reduces future accumulation but requires a live internet connection to read email. Not ideal for frequent travelers.
What Is Safe vs. Not Safe to Delete
| Folder | Safe to delete? | Notes |
|---|---|---|
Mail Downloads/ |
Yes | These are copies; originals stay on the server and in message store |
Containers/com.apple.mail/Data/Library/Caches/ |
Yes (with Mail closed) | Mail rebuilds these automatically on next launch |
~/Library/Mail/V10/ |
No — risky | Deleting this can break your mailbox index; use Mail's own tools instead |
Messages/Attachments/ |
Partially | Safe if you have iCloud Messages sync on; otherwise permanent loss |
After Cleaning: Prevent Mail Storage from Ballooning Again
- Unsubscribe from attachment-heavy newsletters. Marketing emails with embedded images are a major source of silent cache growth.
- Set a reminder to clear Mail Downloads quarterly. The folder silently refills every time you open an attachment.
- Enable Optimize Mac Storage for iCloud Mail if you use iCloud — this offloads older attachments to iCloud automatically.
- Archive large threads to an external drive rather than leaving them in your inbox where Mail caches them locally.
Checking Storage After You're Done
Once you've cleared the downloads and caches, go to Apple menu → System Settings → General → Storage and wait for the bar to refresh (it can take a minute). The "Mail" or "System Data" segment should shrink noticeably. If it still looks high, run the du commands again to confirm the Containers folder reduced in size — macOS Storage graphs are sometimes cached and don't update instantly.
If you want a broader picture of what else is consuming space across your whole Mac, download Crumb and run a whole-Mac audit — it ranks every folder by size so you can see whether Mail, Photos, Xcode derived data, or something else is your next biggest win.
Summary
Apple Mail's hidden containers — especially the Mail Downloads folder and the Containers cache — are the main reason apple mail storage gets out of hand. The Mail Downloads folder at ~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads/ is safe to clear entirely; it holds copies, not originals. The main message store at ~/Library/Mail/V10/ should be managed through Mail's own settings rather than manually deleted. Measure first, delete deliberately, and your Mail footprint can shrink from tens of gigabytes down to a fraction of that in a few minutes.