This is one of the most ubiquitous technologies on the internet and, along with the World Wide Web, is the most used. When you write an email you use a program known as a mailer. When the email is completed it is sent via a number of computers known as email servers and via a number of other intermediate computers before it reaches its destination where it is read. In e-commerce applications email is a subsidiary, but important technology. It is used as the transport medium for mailing lists, for enabling customers to communicate with a company, for sending documents and data to customers and for keeping customers up to date about current products and services. Mailers are sometimes known as mail user agents while mail servers are sometimes known as mail transfer agents.