Be an information provider. Participate in online discussion groups, and be helpful. If you have a World-Wide Web site, provide useful background information about your industry, your specialties, your areas of expertise. This won't help your business and will just get recipients angry. There are much better ways to market your product or service.
Electronic mail is different from postal mail.
For one thing, sending out a conventional direct mail package costs you , the sender. There's nothing to be gained by this. Newsgroups and e-mail discussion groups can be fertile fields for marketing. But watch out. Most groups don't tolerate commercial postings.