In postal mail, the response rate is the percent of people who responded by calling, registering on a website, visiting a store, etc.
In email marketing, the metric "conversion rate" is generally used as the "response" rate. The conversion rate is defined as actions taken as a percentage of unique click-throughs. For a commercial message, an email campaign with the conversion rate 0.25% – 0.50% is rather good. So, actually the email "response" rates often may not be higher than postal mail. But because creating and distributing email messages cost significantly cheaper, email marketing generally brings a much higher return on investment. However, it’s the combination of both postal and email marketing that produces the best results.
You may also hear other lies or misconceptions in email marketing that we didn’t discussed here. As an email marketer, avoid measuring your email campaign performance against the "industry average" and try to make critical campaign decisions based on facts, not assumptions.