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Certified Server Validation




technical method of Email Authentication
intended to fight Spam . Its
focus is the
SMTP
HELO-identity of Mail Transfer Agent s.

CSV was designed to address the problems of
MARID and the ASRG , as defined in detail
as the intent of
Lightweight MTA Authentication Protocol (LMAP)
in an expired
ASRG draft .


PRINCIPLES OF OPERATION


CSV considers two questions at the start of each
SMTP session:

  • Does a domain's management authorize this MTA to be sending email?

  • Do reputable independent accreditation services consider that domain's policies and practices sufficient for controlling email abuse?


CSV answers these questions as follows: to validate an SMTP session from an unknown sending SMTP client using CSV, the receiving SMTP server:

#Obtains the remote IP Address of the TCP connection.
#Extracts the domain name from the HELO Command sent by the SMTP client.
#Queries DNS to confirm the domain name is authorized for use by the IP ( CSA ).
#Asks a reputable Accreditation Service if it has a good reputation ( DNA ).
#Determines the level of trust to give to the sending SMTP client, based on the results of (3) and (4)

If the level of trust is high enough, process all
email from that session in the traditional manner,
delivering or forwarding without the need for
further validation. If the level of trust is too
low, return an error showing the reason for not
trusting the sending SMTP client. If the level of
trust is in between, document the result in a
header in each email delivered or forwarded,
and/or perform additional checks.

If the answers to both of the questions at the top
of this article are 'Yes', then receivers can
expect the email received to be email they want.
Mail sources are motivated to make the answers
yes, and it's easy for them to do so (unless their
email flow is so toxic that no reputable
independent accreditation service will vouch for
them).
CSV is designed to be efficient and elegant, and
in this respect it certainly beats
SPF 's
coverage of HELO identities.


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