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That awesome! I love how our QA work is always free :)
Hmmm, looks like Y! mail is smart enough to strip it out, but I'm sure there is a way around that for someone more creative than myself.
But like Brett mentioned, it could be just one page being sent via email to one or two people.
If you notice hundreds of referrals from Yahoo emails, it sounds more like an Adsenser sending ads via newsletter submission.