Internet Mail Consortium Status of this Memo SMTP Service Extension for Secure SMTP over TLS

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." 1. Abstract This document describes an extension to the SMTP service that allows an SMTP server and client to use transport-layer security to provide private, authenticated communication over the Internet. This gives SMTP agents the ability to protect some or all of their communications from eavesdroppers and attackers. This document is a revision of RFC 2487, which is currently a Proposed Standard. The changes that this draft propose are:-Additional discussion of when a server should and should not advertise the STARTTLS extension (section 5)-More discussion of the man-in-the-middle attacks (sections 5 and 7)-Added section 5.3, STARTTLS on the Submission Port-Bugfix in the example in section 6 to indicate that the client needs to issue a new EHLO command, as already is described in section 5.2. 2. Introduction SMTP [RFC-821] servers and clients normally communicate in the clear over the Internet. In many cases, this communication goes through one or more router that is not controlled or trusted by either entity. Such an untrusted router might allow a third party to monitor or alter the communications between the server and client. Further, there is often a desire for two SMTP agents to be able to authenticate each others' identities. For example, a secure SMTP server might only allow communications from other SMTP agents it knows, or it might act differently for messages received from an