Hvem vil ende i en junk mappe?

SPF allows the owner of an Internet domain to use special format of DNS TXT records
to specify which machines are authorized to transmit e-mail for that
domain. For example, the owner of the example.org domain can designate
which machines are authorized to send e-mail whose sender e-mail
address ends with "@example.org". Receivers checking SPF can reject
messages from unauthorized machines before receiving the body of the message. Thus, principles of operations are quite similar to those of DNSBL, except that SPF exploits the authority delegation scheme of the real Domain Name System.

The sender address is transmitted at the beginning of the SMTP dialog. If the server rejects the sender, the unauthorized client should send a Bounce message
to that address. If the server accepts the sender, and subsequently
also accepts the recipient(s) and the body of the message, it should
insert a Return-Path header in the message''s body in order to save the
sender address. While the address in the Return-Path often matches
other originator addresses in the mail header like "From:" or "Sender:"
this is not necessarily the case, and SPF does not prevent forgeries of
these other addresses.

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Og således implementeres det (igen teknisk da jeg ikke lige har tid til at oversætte, undskyld Martin... men det må vente til lidt senere ;-)

Implementation

Implementing SPF has two parts:

   

• Domains identify the machines authorized to send e-mail on their
      behalf. Domains do this by adding an additional record to their
      existing DNS information.


   

• Receivers can request and use SPF information. They use ordinary
      DNS queries, which are typically cached to enhance performance.
      Receivers then interpret the SPF information as specified and act upon
      the result.

Thus, the key issue in SPF is the specification for the new DNS
information that domains set and receivers use. The records are laid
out like this (in typical DNS-syntax):

example.org. IN TXT "v=spf1 a mx -all"

"v=" defines the version of SPF used. The following words provide mechanisms
to use to determine if a domain is eligible to send mail. The "a" and
"mx" specify the systems permitted to send messages for the given
domain. The "-all" at the end specifies that, if the previous mechanisms did not match, the message should be rejected.