A very, very old email tip to prevent nasty code executions from spam on email clients was to simply disable the preview pane altogether. But you have to remember back then that email clients were decidedly "dumb". Today they’re much smarter. For example, you can disable/enable the preview pane at whim in Mozilla Thunderbird just by pressing F8....

Do I have to say it? Spam. Or at least that’s what Symantec says, so you can take that for what it’s worth. Spam is one of those things that’s constantly changing to bust the roadblocks we put up against it. However we as email users are smarter now and we also have better tools to fight the junk. What’s the best way to filter spam...