The Silent Storage Drain
By default, the Apple Mail application on macOS is configured for maximum convenience, aiming to provide instantaneous access to everything in your inbox. To achieve this, it automatically downloads every single email attachment—PDFs, high-resolution photos, massive presentations—straight to your Mac’s internal hard drive in the background, even if you never actually open the email. If you receive hundreds of emails a day or are part of a corporate mailing list that frequently circulates large assets, this silent background downloading can quickly consume tens of gigabytes of your precious SSD storage without you ever realizing it.
Managing Attachment Downloads
To regain control of your disk space and stop macOS from automatically downloading every email attachment the moment a message hits your inbox, you must change the account behavior within the Mail app settings.
Open the Mail application. Click on Mail in the top-left menu bar and select Settings (or Preferences). A new window will appear. Click on the Accounts tab at the top. On the left side, select the specific email account you want to manage (e.g., your iCloud or Gmail account). In the main panel, look for the dropdown menu labelled Download Attachments. By default, it is set to “All.” Click the dropdown and change the setting to None (or “Recent” if you prefer a middle ground). When set to “None,” Mail will only download the text of the email. You will still see an icon indicating an attachment exists, but it will only download to your hard drive if you explicitly double-click it to open it.