Adding a Wrong Recipient URL for Handling Misdirected Emails

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Table of Contents

1. Introduction

Email recipients today have no clear option as to how to best signal to a provider that they are not the correct recipient of an email. This is a different issue than either an unsubscription request from a mailing list or reporting an email as spam, since the service itself may be a valid sender attempting to reach some user for a valid purpose, but the sender may have inadvertently recorded the wrong email address either due to user error or data entry error.¶

There is collective benefit to all parties if a service is able to detect when an email address is incorrect for a user; the intended recipient, the service, and the inadvertent recipient all prefer correct delivery.¶

Consequently, there ought be a mechanism whereby a service can indicate it has an endpoint to indicate a "wrong recipient" of an email. If this header field is present in an email message, the user can select an option to indicate that they are not the intended recipient.¶

Similar to one-click unsubscription [RFC8058], the mail service can perform this action in the background as an HTTPS POST to the provided URL without requiring the user's further attention to the matter.¶

Since it's possible the user may have a separate valid account with the sending service, it may be important that the sender be able to tie which email was sent to the wrong recipient. For this reason, the sender may also include an opaque blob in the header field to specify the account ID referenced in the email; this is included in the POST.¶

Note that this kind of misdelivery shouldn't be possible if a service has previously verified the user's email address.¶

2. Conventions and Definitions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

3. High-Level Goals

Allow a recipient to stop receiving emails intended for someone else.¶

Allow a service to discover when they have the wrong email for a user.¶

4. Out of Scope

This document does not propose a mechanism for automatically discovering whether a given user is the correct recipient of an email, though it is possible to use some of the signals in an email, such as the intended recipient name, to infer a possible mismatch between actual and intended recipients.¶

5. Implementation

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 [RFC7489], that provides a domain-level identifier in the content of the "d=" tag of a validated DKIM-Signature header field.¶

The Wrong-Recipient header field needs to be included in the "h=" tag of a valid DKIM-Signature header field.¶

7. Examples

Header in Email¶

Wrong-Recipient: <https://example.com/wrong-recipient?uid=12345&email=user@example.org>

Resulting POST request¶

POST /wrong-recipient?uid=12345&email=user@example.org HTTP/1.1
Host: example.com

8. Security Considerations

The Wrong-Recipient header field will contain the recipient address, but that is already exposed in other header fields like To:.¶

The user ID of the recipient with the sending service may be exposed by the Wrong-Recipient URI, which may not be desired but a sender may use an opaque blob to perform a mapping to a user ID on their end without leaking any information to outside parties.¶

A bad actor with access to the user's email could maliciously indicate the recipient was a Wrong Recipient with any services that used this protocol, causing mail delivery and potentially account access difficulties for the user.¶

9. IANA Considerations

IANA will be requested to add a new entry to the "Permanent Message Header Field Names" registry.¶

Header field name: Wrong-Recipient
Protocol: mail
Status: Provisional
Author/Change controller: IETF
Specification document(s): *** This document ***
Related information: none

Acknowledgments

Many thanks to John Levine, Oliver Deighton, and Murray Kucherawy for their kind and actionable feedback on the language and proposal. Thanks to Eliot Lear for helping guide the draft to the right hands for review.¶

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