I was wrong. From the submission page:
Begin with a query letter describing your project, background, and credentials, which you may send by mail or e-mail. If you wish to receive a hard copy reply you must include a self-addressed, stamped envelope.
For this first contact, nothing should be enclosed with the letter; don’t send any sample material until we advise you that we’d like to see it. E-mails with unsolicited attachments will be deleted unread, out of concern for viruses.