Some e-mails will add you to some sort of botnet the moment you read the mail (I'm not actually sure if this is a botnet, but I receive spam mails from regular people all the time. So I assume it is). But it's sometimes hard to tell which e-mails are legitimate and which aren't. Hotmail offers an option to look at the e-mail source, from which I can easily make up if it's legitimate. But I'm wondering if you're safe when only reading the source?
As a clarification, the "source" is the plain text e-mail. I'm using hotmail in Waterfox 12.