Self-mailers in B2B Direct Mail: Advantages and Disadvantages

Business-to-business direct mail marketers have learned through testing that a letter in an envelope will usually generate more sales and pull more inquiries than a self-mailer will. Why is that? And on what occasions are you wise to use a self-mailer instead of a letter? A self-mailer, of course, is any flat piece of mail that arrives at its destination without an envelope. It mails "by itself," and so has no need of an envelope. Postcards, strictly speaking, are self-mailers, but the kind of self-mailers I am talking about here are the ones that have a fold in them. A classic self-mailer is a sheet of card stock, 8