Email auto responders are a powerful tool that can be used to automate a variety of tasks, such as welcoming new subscribers, nurturing leads, and sending out promotional offers. But how did email auto responders come about? Procmail and Sieve The earliest email auto responders were created using procmail and Sieve, which are both powerful mail filtering tools. Procmail is a command-line tool that can be used to create complex filtering rules, while Sieve is a scripting language that is designed specifically for filtering email.