Mule ESB is an integration platform that allows applications to connect and exchange data regardless of technology. This document discusses using Mule ESB to send an email with an attachment. It describes using a file inbound endpoint to read a file from a source directory, an attachment transformer to add the file content as an attachment, and an SMTP outbound endpoint to send the email. Running the Mule application results in the file content being sent as an attachment in an email.