Vouch by Reference

Vouch by Reference provides a mechanism for some entity (an email certification provider) to tell a receiving mail system about the reputation of a sender of email. It is intended to become a standard way for email certification providers to vouch for outbound email sent by others, and is described in an Internet Draft [http://tools.ietf.org/html/draft-hoffman-dac-vbr] . VBR information can be used by a Mail Transfer Agent, a Mail Delivery Agent or by an email client.

How VBR Works

The email sender

A customer of a VBR Email Certification Provider signs their message using DomainKeys Identified Mail, including within the list of signed headers a VBR-Info: header field. This VBR-Info: header field contains

* the VBR Email Certification Provider's domain name,
* the type of content in the message, and
* a list of domain names of services that the sender expects to vouch for the sender for that kind of content.

The email receiver

Using DKIM, an email receiver can verify that the message is properly signed (thus verifying the domain that send the message). It can then verify, using DNS, that the vouching service actually vouches for that type of content for that domain.