Apple Mail Security: Disable Loading of Remote Content
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Spammers like to send emails with tiny 1 X 1 pixel images; if the image is loaded, they know they have a “live one”. Don’t do this to yourself, it’s just inviting more spam. But it need not be hidden; any remote content in an email serves the same “live one” purpose.
Make sure thebox is unchecked as shown below.
When reading a mail message, you can alwaysin any particular email by clicking the button at the top right of the mail message.
Tip: another way to detect if a message is a scammer is to display extra message headers. These often reveal skanky details that are a big red flag.