Mail downloads and System Data
Updated · Dmytro Virych
Attachments Mail saved a second copy of. The originals stay in your mailbox. The copies live in Mail's own container in your Library and count as System Data.
What Mail downloads are
When you open or preview an attachment in Mail, the app writes a copy of it to a downloads folder inside its container so it can hand the file to Preview, Quick Look or another app. The message still holds the original. Mail does not clear the copy afterwards by default, so every attachment you have ever opened is still there.
Each copy sits in its own folder named by a long identifier, with the attachment inside under its real name. That is why several folders can hold a file with the same name: the same calendar invitation opened from five messages is five copies.
Why removing the copies is safe
Because they are copies. The attachment you care about is the one attached to the message, and that stays exactly where it is. Open the attachment again and Mail writes a fresh copy.
The folder to be careful of is the one beside the downloads. Mail’s mailboxes live under ~/Library/Mail, and the attachments in there are the mail itself: for an account that stores mail on a server they would download again, but for a POP or local account they are the only copy. A guide, or a cleaner, that points you at that folder is asking you to delete mail. This page does not, and neither does MacMemory.
How to stop Mail keeping copies
Mail's settings let you choose how much it downloads per account. Open Mail, choose Settings, then Accounts, select an account and look under Account Information for the attachment setting. Choosing to download only recent attachments, or none, keeps the copies folder small from then on. Attachments you open are still fetched when you ask for them.
This does not remove what is already in the folder. The steps below do.
How MacMemory shows them
Listed under Mail downloads with the label Safe to delete, each row named after the attachment inside it with the date it was downloaded. Ticked rows go to the Trash. The category needs Full Disk Access to be read, and until that is granted the row shows a lock rather than a size, because a folder the app cannot open is not empty.
How to clear Mail's attachment copies by hand
One folder, in Finder. Quit Mail first so it is not writing to the folder while you empty it.
Quit Mail. Safe to delete
Choose Mail, then Quit Mail, or press Command-Q with Mail in front.
Undo: Nothing is removed at this step.
Open the downloads folder. Safe to delete
In Finder, choose Go, then Go to Folder, and paste the path below. This is the copies folder, not the mailbox.
Location:
~/Library/Containers/com.apple.mail/Data/Library/Mail DownloadsUndo: Nothing is removed at this step.
Move the contents to the Trash. Safe to delete
Select everything in the folder and move it to the Trash. Leave the folder itself in place. Reopen Mail; every message still has its attachment.
Undo: In the Trash until you empty it. Opening an attachment in Mail again makes a fresh copy.
The shortcut
MacMemory does the steps above from one screen. It scans for free, lists what it finds with one plain sentence per row and the same two labels — Safe to delete and You decide — and moves what you tick to the Trash. Four exceptions are stated on the row that offers them: Time Machine snapshots, the Trash itself, Docker images, which only Docker can remove, and unused simulators, which only Xcode can erase, are removed outright. Mail, backups, snapshots and the Trash need Full Disk Access to be read at all, and a category it cannot read shows a lock rather than a zero.
Nothing it deletes is beyond what this page describes. What it saves you is the Terminal. What it costs · Questions people ask