Email 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 content header's From: field to indicate the author of the message and the Sender: field to indicate who initially handled the message, on the author's behalf. 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. 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. Terminology and architectural details in this document are incorporated from . Discussion of this draft is directed to the ietf-822@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 for the field's syntax is:

author = "Author:" mailbox-list CRLF which echos the syntax for the From: field. 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. X-Original-From: is a similar header field, referenced in . However it 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. Generally, the handling of the Author: header field needs to receive scrutiny and care comparable to that given to the From: header field, but preferably not in a way that defeats its utility. 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.

The Author header field is registered, per Header field name: Author Applicable protocol: mail Status: Standard Author/Change controller: Dave Crocker ⟨dcrocker@bbiw.net⟩ Specification document(s): *** This document ***

Given that the semantics of this field echo the long-standing From: field, the basic mechanics of the field's creation and use are well understood. Points of concern, therefore, are with possible interactions with the existing From: field, with anti-abuse systems, and with MUA behavior, along with basic market acceptance. So the questions to answer, while the header field has experimental status are: Is there demonstrated interest by MUA developers? If MUA developers add this capability, is it used by authors? Does the presence of the Author field, in combination with the From field, create any operational problems, especially for recipients? Does the presence of the Author field demonstrate additional security issues? Does the presence of the Author field engender problematic behavior by anti-abuse softwere, such as defeating its utility?