E-mail has become the dominant technique for marketing face-to-face events. Here is the latest:
Industry best practice is that the recipient must proactively agree to receive your messages. Does this mean that Widget Expo '03 attendees have opted in to receive promotion e-mails regarding Widget Expo '04? No—you must get them to "re-up" for next year. One month after this year's show, send them an e-mail highlighting next year—and ask if it is OK to keep them informed about the show. Always provide an opt-out clause at the end of each e-mail.
Be wary of the various anti-spam initiatives that are being undertaken. Many may restrict your ability to use blast e-mails to reach your target audience. For example, more and more corporations are taking drastic steps to block unwanted e-mails. Be sure your e-mails are not considered spam. They should provide valuable information and not simply say "come to the show."
Good news—you can conceive a blast e-mail on Monday, send it Monday night and get immediate results by noon Tuesday. Bad news—an e-mail has no shelf life, so response will be nil after noon on Wednesday. Be sure your e-mails demand immediate action—and make it easy to take that action (such as providing a link directly to your simple registration form).
HTML or Text-only?
Don't use HTML: your audience prefers text-only because many of them are now reading their e-mails on Blackberry or cell phones. Plus, you never have to worry about browser incompatibility. The benefit of HTML is not worth the down side.