- By default most Mail tools download images embedded in HTML mail. Apple’s Mail tool does, and Leopard’s new Mail templates can only increase this tendency.
- By embedding images with unique URLs into spam, spammers can discover which email addresses are used.
- By sending emails that are clearly spam and emails that are unlikely to be spam, a spammer can determine whether you have a spam filter.
- By sending emails that could be spam, but also could match terms in your email, a spammer can determine what other email is in your mailbox, thus for instance what your political opinions are.
This could provide an alternative explanation for the recent rash of weird spam not selling anything.