Author Header Field

Internet mail conducts asynchronous communication from an author to one or more recipients, and is used for ongoing dialogue amongst them. Email has a long history of serving a wide range of human uses and styles, within that simple framework, and the mechanisms for making email robust and safe serve that sole purpose. Internet mail defines the From: field to indicate the author of the message's content and the Sender: field to indicate who initially handled the message. The Sender: field is optional, if it has the same information as the From: field. That is, when the Sender: field is absent, the From: field has conflated semantics, as both a handling identifier and a content creator identifier. These fields were initially defined in and making the redundant Sender: field optional was a small, obvious optimization, in the days of slower communications, expensive storage and less powerful computers. The dual semantics was not a problem, until development of stringent protections on use of the From: field. It has prompted Mediators, such as mailing lists, to modify the From: field, to circumvent mail rejection caused by those protections. This affects end-to-end usability of email, between the author and the final recipients, because mail received from the same author is treated differently by the recipient's software, depending on what path the message followed. Because the current email protection behavior involves the From: field, it is common to think that the issue, in protecting the field's content, is behavior of the human recipient. However there is no indication that the enforced values in the From: field alter end-user behavior. The meaningful protections actually operate at the level of the receiving system's mail filtering engine, which decides on the dispostion of received mail. By way of example, mail from "Example User <user@example.com>" which is sent directly to a recipient, will show the user's display name correctly and can correctly analyze and aggregate mail from that user, based on their email address. However if the user sends through a mailing list, and the mailing list conducts a common form of From: modification, needed to bypass enforcement of stringent authentication policies, then the received message might have a From: field along the lines of "Example User via Example List <listname@list.example.com>". The change inserts an operational address, for the Mediator, into the From: field, and distorts the field's display-name, as a means of recording the modification. The result is that the recipient's software will see the message as being from an entirely different author and will handle it separately. (Mediators might create a Reply-To: field, with the original From: field email address, but this does nothing to aid other processing done by the recipient's MUA based on what it believes is the author's address or original display-name. In effect, the From: field has become dominated by its role as a handling identifier. The current specification augments the current use of the From: field, by specifying the Author: field, which identifies the original author of the message and is not subject to modification by Mediators. While it might be cleanest to move towards more reliable use of the Sender: field and then to target it as the focus of authentication concerns, enhancement of standards works best with incremental additions, rather than efforts at replacement. To that end, this specification provides a means of supplying author information that is not subject to modification by processes seeking to enforce stringent authentication. Teminology and architectural details in this document are incorporated from Discussion of this draft is directed to the dmarc@ietf.org mailing list.

A new message header field is defined: Author:. It has the same syntax as From:. As with the original and primary intent for the From: header field, the Author: header field is to contain the email address and can contain the displayable human name of the author for the message content. The ABNF for the field's syntax is:

author = "Author:" mailbox-list CRLF This header field can be added as part of the original message create process, or it can be added later, to preserve the original author information from the From: field.

The Author: header field, here, is intended for creation during message generation or during mediation. It is intended for use by recipient MUAs, as they typically use the From: field. In that regard, it would be reasonable for an MUA that would normally organize or display information based on the From: field to give the Author: header field priority. The X-Original-From: header field is referenced in but is not actually defined. Further, it is registered with IANA, but the registry cites RFC5703 as the controlling source for the entry. Lastly, the field is solely intended for use by Mediators, to preserve information from a modified From: Obviously any security-related processing of a message needs to distinguish From: from Author: and treat their information accordingly.

Any header field containing identification information is a source of security and privacy concerns, especially one pertaining to content authorship. At a minimum, the handling of the Author: header field needs to receive the same scrutiny and care given to the From: header field. Given the semantics of this field, it is easy to believe that use of this field will create a new attack vector for tricking end-users. However, for all of the real and serious demonstration of users' being tricked by deceptive or false content in a message, there is no evidence that problematic content in a field providing information about message's author directly contributes to differential and problematic behavior by the end user.

Header field name: Author Applicable protocol: mail Status: provisional Author/Change controller: *** ??? *** Specification document(s): *** This document ***