The Invisible Storage Drain
The default Apple Mail application on macOS is configured to provide a seamless offline experience. To achieve this, it will often automatically download all incoming email attachments—including massive PDF reports, high-resolution photo galleries, and video files—directly to a hidden folder deep within your Mac’s Library. If you receive hundreds of emails a day and only need to read the text, this automated behavior will silently consume gigabytes of precious hard drive space over time, eventually leading to “Disk Almost Full” warnings even if your visible Downloads folder is completely empty.
Restricting Attachment Caching
To preserve your local storage capacity and stop macOS from automatically downloading every single Mail attachment, you must restrict the application’s account preferences.
Open the Mail application. Navigate to the top menu bar, click on Mail, and select Settings (or Preferences on older versions of macOS). In the settings window, 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). On the right side, click on the Account Information tab. Look for the dropdown menu labelled Download Attachments. By default, this is often set to “All.” Click the dropdown menu and change it to None or Recent. (If you select “None,” you will still be able to download attachments manually by clicking on them within the individual email when you actually need them).