Bulk email marketing and spamming are cousins from the same family of online marketing because both are fundamentally trying to advertise a product or service. The fundamental difference between them is the difference between a proper advertising campaign and a two line post-it. Most spam mail is fundamentally a hard-sell, unappealing mail that is sent out with the humble flyer as a design benchmark. Sending bulk emails to potential buyers cannot be done this way anymore and especially since TV advertising is still a force to be reckoned with. There is nothing to stop a bigger competitor from wiping a small company off the face of the earth because of bad advertising methods. Therefore, design, ingenuity, and interactivity are becoming the buzzwords for those who send bulk emails. Design is also a complicated issue that requires time and investment: investment in the form of designers and content writers. Design also means that one needs to possibly invest in mail design templates to make the process of mailing consistently simpler. Notice how spammers will never take this route. This coupled with more ethical means of email address harvesting results in a clear distinction between you and a spammer.
Bulk email marketing and advertising are almost the same. Therefore the design rules for both remain relatively the same. Most serious bulk email campaigns have a common theme graphically and contextually and this is the first design guideline that one needs to follow. This differentiates the product from its competition, from its fellow brands, and other competing products.
Using multimedia when sending bulk emails is not a regular practice but with the increasing number of people using broadband, this will be a medium that will eventually rival TV advertising. Therefore, use a video embedded in the mail if possible.
Minimalism; this is one concept that has not caught on sensibly on the internet primarily because people consider it a medium of text. This is one mistake that you should not make. When you send bulk emails, ensure that textual content is kept at a bare minimum and that you use more imagery.
Interactivity is another key design component. People like to click and figure out their own way through a promotion exercise and to that effect, insert links in your mail that point to exact sections that a customer would like to view.
At the end of the day, however, bulk email marketing or sending bulk emails is still a fight against spam filters and junk email folders. Therefore, also ensure that you get customers to opt-in before you send bulk emails to customers. This is not only required legally but is also a more ethical practice to follow. Make it point to analyze the details of the CAN SPAM act.