E-mail security becomes critical issue to research community in the field of information security. Several solutions and standards have been fashioned according to the recent security requirements in order to enhance the e-mail security. Some of the existing enhancements focus on keeping the exchange of data via e-mail in confident and integral way. While the others focus on authenticating the sender and prove that he will not repudiate from his message. This paper will survey various e-mail security solutions. We introduce different models and techniques used to solve and enhance the security of e-mail systems and evaluate each one from the view point of security.