OMX records: Outgoing Mail eXchanger


We propose that all entities that send e-mail publish
an A record in their DNS, with a name "omx" which lists
the machines that legitimate e-mail from users with
addresses in that domain comes from.  For instance,
if mindtrust llc owns the mindtrustllc.com domain, and
sends mail out through a MTA located at IP address 1.2.3.4,
mindtrust LLC would add an address record in their DNS
for omx.mindtrustllc.com and list 1.2.3.4 in that record.

Domains that use multiple boxes for their outbound sending,
such as yahoo, would list all the outgoing IP addresses in
their omx address record.

The RAPNAP system, when queried about a sender,IP pair,
can then look up the omx machine in the  sender's domain
and if the IP is listed there, the RAPNAP system can
skip a more complex verification step.

( Added 30 september 2003:)
The existence of an OMX.example.com record is taken to indicate that
the payment preferences of postmaster@example.com are
inherited by users@example.com, regarding SMTP mail originating
at a address listed as an OMX.  Furthermore, users@example.com
are allowed to draw sender-pay micropayments from the
postmaster@example.com sending account, within limits
established as part of the postmaster account record, if it exists
within the pay2send system.