I don't think this can work well, especially since most of us are tired of receiving spam. And, if you haven't received permission to send them an advertising email, you are actually spamming.
Try to be active in forums and blogs, with your link in the signature. Make sure the portfolio looks great and people will visit it and be impressed. I got a LOT of work this way, since people would trust me better than if I was to email them. Promote a lot offline, pay for an adword campaign (or ads on other sites) if you can convert to good clients. You can also create an account on some freelancing sites, you are paying a commission to get jobs through them, but it can surely help with slower periods.