Signalling one-click functionality for list email headers
draft-levine-herkula-oneclick-02

Abstract

This document describes a method for signaling a one-click function for the list-unsubscribe email header. The need for this arises out of the actuality that mail software sometimes fetches URLs in mail headers, and thereby accidentally triggers unsubcriptions in the case of the list-unsubscribe header.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on January 23, 2017.

Copyright Notice

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Table of Contents

• 1. Introduction
• 2. Definitions
• 3. High-Level Goals
• 4. Out of Scope
• 5. Implementation
• 5.1. Mail senders
• 5.2. Mail receivers
• 6. Additional Requirements
• 7. IANA Considerations
• 8. Examples
• 8.1. Simple
• 8.2. Complex
• 9. Security Considerations
• 10. Normative References
• Authors' Addresses

1. Introduction

An [RFC2369] email header can contain HTTP or HTTPS URIs. In a List-Unsubscribe Header the HTTP or HTTPS URI is intended to unsubscribe the recipient of the email from the list. But anti-spam software often fetches all resources in mail headers automatically, without any action by the user. As a result of this unintended malicious behavior, senders implement landing pages with a confirmation step to finish the unsubscribe request. This document addresses this part of the problem, with a POST action for receivers that can be distinguished by senders from other requests and therefore handled as a one-click unsubscription.

2. Definitions

The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

One-click describes an action that directly triggers a change in a system's state, intended to be applied only with a user's intent.

3. High-Level Goals

This document has several goals.

• Allow email senders to signal "One-Click" functionality for specific HTTP and HTTPS URIs used in [RFC2369] email headers.
• Allow MUA designers to implement independent user interface features for a better user experience.
• Allow MUA users to trigger intended actions in a familiar environment and without leaving the MUA context.

4. Out of Scope

This document does not address problems associated with intended malicious behavior.

5. Implementation

5.1. Mail senders

An entity which is responsible for sending an email that wishes to add an HTTP or HTTPS URI for one-click unsubscriptions places both a List-Unsubscribe and a List-Unsubscribe-Post header in the message. The List-Unsubscribe-Post header may contain multiple key value pairs needed by the sending entity. It also MUST contain the key value pair "List-Unsubscribe=One-Click".

The combination of the URI in the List-Unsubscribe header and the POST arguments in the List-Unsubscribe-Post header MUST identify the mail recipient, so that the unsubscription process knows what address to handle. In particular, "one click" has no way to manually ask the user what address he or she wishes to unsubscribe.

The sending entity needs to provide the infrastructure to handle POST requests to the specified URI in the List-Unsubscribe header.

The "One-Click" action triggered by this URI SHOULD complete promptly and not burden the requester in an inappropriate way. The sending entity cannot expect that HTTP redirects are followed by the requester.

5.2. Mail receivers

A receiving entity which wants to use a List-Unsubscribe HTTP URI from an email that also contains a List-Unsubscribe-Post header performs an HTTP or HTTPS POST to the first HTTP or HTTPS URI in the List-Unsubscribe header and send the content of the List-Unsubscribe-Post header as the request body.

The POST content SHOULD be sent as "multipart/form-data" [RFC7578] and MAY be sent as "application/x-www-form-urlencoded". These encodings are the ones used by web browsers when sending forms. The target of the POST action will typically be the same as or similar to the one in the confirmation page when doing a manual two-click unsubscribe, so this is intended to allow the same server code to handle both.

The receiving entity MUST NOT perform a POST on the the HTTP or HTTPS URI without user consent. When and how the user consent is obtained is not part of this specification.

The Request uses the HTTP or HTTPS verb POST. The HEAD and GET requests are not intended to be used to trigger a state change. PUT and DELETE would offer similar functionality but are often unavailable.

6. Additional Requirements

The email needs at least one valid authentication identifier. In this version of the specification the only supported identifier type is DKIM [RFC6376], that provides a domain-level identifier in the content of the "d=" tag of a validated DKIM-Signature header field.

The List-Unsubscribe and List-Unsubscribe-Post headers need to be included in the "h=" tag of a valid DKIM-Signature header field.

[[ what is the intention of this next rule? ]]

The domain used in the HTTP or HTTPS URI MUST be the domain in the "d=" tag of a valid DKIM-Signature header field in which the headers are included in the "h=" tag.

7. IANA Considerations

IANA is requested to add a new entry to the Permanent Message Header Field Names registry.

Header field name: List-Unsubscribe-Post

Applicable protocol: mail

Status: standard

Author/Change controller: IETF

Specification document: this document

8. Examples

8.1. Simple

Header in Email

List-Unsubscribe: <https://example.com/unsubscribe.html>
List-Unsubscribe-Post: List-Unsubscribe=One-Click&recip=user@example.com

Resulting POST request

POST /unsubscribe.html HTTP/1.1
Host: example.com
Content-Type: application/x-www-form-urlencoded
Content-Length: 49

List-Unsubscribe=One-Click&recip=user@example.com

8.2. Complex

Header in Email

List-Unsubscribe: <mailto:listrequest@example.com?subject=unsubscribe>,
    <https://example.com/unsubscribe.html?campaign=123456789>
List-Unsubscribe-Post: List-Unsubscribe=One-Click

Resulting POST request

POST /unsubscribe.html?campaign=123456789 HTTP/1.1
Host: example.com
Content-Type: application/x-www-form-urlencoded
Content-Length: 49

List-Unsubscribe=One-Click&recip=user@example.com

9. Security Considerations

The List-Unsubscribe-Post header will typically contain the recipient address, but that address is usually also in the To: header. This specification allows anyone with access to a message to unsubscribe the recipient of the message, but that's typically the case with existing List-Unsubscribe, just with more steps.

10. Normative References

Authors' Addresses