Mail Downloads folder on Mac: safe to delete attachments?

What it is

When you open an attachment in Apple Mail, Mail writes a copy to the Mail Downloads folder inside its sandbox container so other apps can open it. These are working copies, not the attachments stored with your messages.

Why it gets so big

Every attachment you've opened can leave a copy behind, and large PDFs, images and videos add up over time.

Is it safe to delete?

Yes. Attachments remain in the emails themselves, on the server for IMAP and Exchange accounts or in Mail's local store. Opening one again simply recreates the copy. Quit Mail first. One catch: if you edited an opened attachment and saved it in place, that edited version may only exist here, so move it somewhere safe before clearing.

Tip

Mail's message store in ~/Library/Mail is usually much bigger; the Download Attachments option in each account's settings controls how much of it is kept on your Mac.