Bounce Address Tag Validation (BATV)
“Was use of the bounce
address authorized?”

D. Crocker

Brandenburg InternetWorking

mipassoc.org/batv

03/08/05 13:12

MIPA

Basic Email Roles

Envelope – Mail-From Content – Return-Path

Return address (bounces)

Content – Received header

Receiving Relay

Sending Relay

Submitter into transfer service

Originator (author)

Who

Content –
From/Resent-From

Envelope – HELO/EHLO
Content – Received header

Content –
Sender/Resent-Sender

Specified in

Bounce Addresses Abuse

Redirecting flood of bounces

Spam sends to many invalid addresses, thereby causing masses of bounces.

Spammers specify stray bounce addresses – like yours -- just to get the traffic off the sending service

Backdoor trojan

Bounce message, itself, might contain dangerous content

Denial of service

The flood of messages can cripple the bounce receiving site

Evaluation Venues

MTA

MDA

MTA

MTA

MSA

Bounce

Receipt

Bounce

Generation

Bounce

Generation

MDA

MTA

Sign
MailFrom

Intermediate
Relay

Bounce Address Validation Goals

Bounce recipient delivery agent

Should I deliver this bounce?

Bounce originator

Should I create this bounce?

And by the way…

If the bounce address is invalid, the entire message is probably invalid

If we can detect forged mail, we do not need to worry about its bounce address

BATV

Sign envelope Mail-From address

Protect against simple bounce address forgery

Possibly protect against unauthorized re-use of signature

Submission Agent adds sig to bounce address

MAIL FROM mailbox@domain 

MAIL FROM sig-scheme=mailbox/sig-data@domain

Multiple signature schemes

Symmetric – can only be validated by signer’s admin

Public – can be validated by relays on original path

A Symmetric BATV Signature

Originating site uses any signing scheme

BATV spec provides a simple version

joe-user@example.com 

prvs=joe-user/tag-val@example.com

tag-val =	Encryption of
(day address will expire,
original mailbox@domain)

Public BATV Signature

Same style as for symmetric key approach

Except that originating site uses symmetric key and the evaluating site must obtain the public key

Public key distribution is the core difficulty

Therefore, piggyback the effort on an existing message encryption effort, like DomainKeys and Identified Internet Mail

Unfortunately, no existing public key-based message signing effort has widespread support… yet

Status

Several rounds of specification and open comment

Now recruiting field experience

Plan to pursue IETF standardization

To follow-up…

Mailing list

http://mipassoc.org/mailman/listinfo/ietf-clear

BATV specification

http://ietf.org/internet-drafts/…

Bounce Address Tag Validation (BATV)
draft-levine-mass-batv-00.txt

Internet mail architecture

http://bbiw.net/current.html#email

draft-crocker-email-arch-03.txt

Introduction to CSV

Dave Crocker

2004-10-28T12:25:36