That 'Mail Downloads' Folder Is Why Your Mail Is Silent — and 10GB+

Mail.app has a dirty little secret: every attachment you’ve opened is copied into ~/Library/Containers/com.apple.mail/Data/Library/Mail Downloads, and it stays there after you delete the email.

Open a few business PDFs, a client’s deck, a video someone “just sent by email,” and that folder is quietly 5–20 GB of stuff you’ve already read (or never needed at all). It’s also one reason your Mac feels full while your “important files” folder is tiny.

Find the real size

du -sh ~/Library/Containers/com.apple.mail/Data/Library/'Mail Downloads'/*

And the sub-accounts’ listing (each mailbox bundle has its own):

find ~/Library/Containers/com.apple.mail/Data/Library -iname '*Downloads*' -maxdepth 3 -type d

You’ll often see a few gigs in Mail Downloads/<account>/ — every attachment is cached there per mailbox.

Safe to delete? Yes — here’s the catch

The downloads cache is a cache: you can safely remove it wholesale. The one nuance: if you delete these files while Mail is open, connections to open attachment previews can flicker until you reopen them. So:

The clean routine:

1. Quit Mail entirely (⌘Q).
2. Delete the cache:

rm -rf ~/Library/Containers/com.apple.mail/Data/Library/'Mail Downloads'

3. Reopen Mail. It re-fetches any attachment you actually open again — from the server or your mailbox store — on demand.

Does this delete my emails? No. The messages themselves, folders, drafts, sent, all live in your mailbox store (Mail/V3). The Mail Downloads folder is purely the opened-attachment cache. You lose nothing except cached copies.

Why it never shrinks on its own

Mail has no “clear attachment cache” setting. The folder grows with each attachment you preview (including the inline-image-preview downloads some clients do), and it never prunes. That’s by design-ish — it makes opening attachments feel instant — but it turns a hidden folder into the most under-diagnosed disk hog on consumer Macs.

The better long-term fix

If your Mail archives matter and attachments are big, add a recurring habit:

• Every couple of months: quit Mail → rm -rf 'Mail Downloads'.
• In Settings → Mail → add nothing — there’s no official toggle. So make the periodic clean a habit, or use a disk tool that flags it by size.

Find the rest of the bloat while you’re at it

The Mail Downloads folder is a classic “hidden folder in a container,” exactly like:

• ~/Library/Developer/CoreSimulator (guide)
• ~/Library/Caches (guide)
• Docker.raw (guide)

A disk map that includes hidden/container paths shows all of them at once — which is how you fix a full disk without guessing.

How DiskInsight helps here

DiskInsight scans your home folder including the ~/Library/Containers tree, so Mail Downloads shows up as a named, byte-sized block instead of invisible noise. You see it, you decide, it’s staged to the Trash for review — nothing is auto-deleted, and Mail’s real data (your messages) is never offered up.

100% local, no telemetry, no account, one-time price.

TL;DR

1. du -sh ~/Library/Containers/com.apple.mail/Data/Library/'Mail Downloads' — see it.
2. Quit Mail.
3. rm -rf .../'Mail Downloads' — clear the cache (safe).
4. Re-fetch any attachment you genuinely open later from the server.

Your emails are untouched; the attachment cache is gone.

Get DiskInsight Pro · $9.99 one-time to find Mail Downloads and the other hidden gigabytes on one screen. Full guide: free up space on a Mac.