not a lot of people know how to email properly - there is always a sales pitch - and usually I just filter them right away
Email marketing is legal and it converts well. However you may have to ensure that you compiled the list ethically else you may be spamming. One of the best ways is to ask your visitors to opt in to ezines or make subscriptions so you send them peiodic newsletters. To start an ezine, get topics around the main theme of your site and then ask your visitors to opt in. Ocassionally, send them updates or information of interest to them. Do not hard sell but make recommendations about the products or services you want to offer.