Mail Taking Up Space on Mac? Clear Attachment Storage

Apple Mail keeps a local copy of every message — and, depending on one setting, every attachment — across all your accounts. On a mail-heavy Mac that store runs to many gigabytes. You can trim it hard without losing a single message, because IMAP and iCloud accounts keep the originals on the server.

See how much space Mail is using

Mail's local store lives at ~/Library/Mail. In Finder, press ⇧⌘G, paste that path, then select the folder and press ⌘I for Get Info. Or from Terminal:

# Check the size of Mail's local message store (read-only)
du -sh ~/Library/Mail

You'll also find a Mail row in System Settings → General → Storage. A few hundred megabytes is normal; tens of gigabytes means years of cached attachments worth trimming. To spot the individual culprits, open Mail, select a mailbox, and choose View → Sort By → Size — the messages carrying huge attachments float straight to the top, and you can delete the disposable ones right there.

Stop caching every attachment

By default Mail can download every attachment in every message it syncs. One setting per account controls this:

1. Open Mail, then Mail → Settings (⌘,) and click Accounts.
2. Select an account and stay on the Account Information tab.
3. Set Download Attachments to Recent or None.

Attachments stay on the server and download on demand the moment you open a message, so you lose nothing — just the pre-caching. To undo, set the menu back to All. Note this governs future syncing; already-cached attachments stay on disk until the account re-syncs (see the last section). Repeat for each account in the sidebar — the setting is per account, and it's usually the work address with a decade of PDFs that needs it most.

Erase junk and deleted messages

Junk and Trash still occupy disk until they're actually erased. Two menu commands do it on demand: Mailbox → Erase Junk Mail and Mailbox → Erase Deleted Items → In All Accounts…. To make it automatic, go back to Mail → Settings → Accounts, pick an account, open the Mailbox Behaviors tab, and set junk and deleted messages to be erased after a day, a week, or a month. Undo by setting them back to Never — though messages already erased don't come back. On accounts that receive heavy newsletter traffic, this pair of settings alone keeps gigabytes from accumulating.

Rebuild a bloated account

Don't delete folders inside ~/Library/Mail by hand. Mail's database index will disagree with what's on disk, mailboxes can appear empty or corrupted, and for POP accounts those files are the only copy of your mail. The clean way to shed years of cache:

1. Open System Settings → Internet Accounts and select the account.
2. Turn the Mail toggle off. The local cache for that account is removed.
3. Turn it back on. Mail re-syncs from the server, honoring your new Download Attachments setting.

This is safe for IMAP, iCloud, Gmail, and Exchange — the server keeps everything. Skip it for POP accounts, where messages may exist only on your Mac. Expect the first re-sync to take a while on a large account; Mail downloads headers first, so the mailbox is usable long before the cache finishes rebuilding.

One more quiet space eater: every attachment you open or quick-look from Mail can also end up saved in Downloads. If you habitually double-click attachments, your ~/Downloads folder is carrying a second copy of years of PDFs — worth a sweep while you're at it.

Mail isn't the only hoarder

Everything under ~/Library/Mail is billed to System Data in the storage bar, alongside caches from Messages, browsers, and developer tools. If the number still looks wrong after this cleanup, see what else hides inside System Data.