This document discusses using email interfaces for Ruby applications. Some key points covered include: - Email is ubiquitous and can provide inherent attention and gradual engagement. It also allows embedding identity and resurrecting dead data. - Elements of an email interface include the TO address, subject line, message body, and attachments. - Receiving email involves tools like Postfix and POP/IMAP for fetching messages, then processing them using libraries like TMail and mms2r. - Testing email interfaces requires fixtures to ensure proper functionality.