Electronic mail (email) is perhaps the most popularly used system for exchanging business information over the Internet (or any other computer network). At the most basic level, the email process can be divided into two principal components: (1) mail servers, which are hosts that deliver, forward, and store email; and (2) mail clients, which interface with users and allow users to read, compose, send, and store email. This document addresses the security issues of mail servers and mail clients, including Web-based access to mail.