The Problem: Sender Address Forgery
Today, nearly all abusive e-mail messages carry fake sender addresses. The victims whose addresses are being abused often suffer from the consequences, because their reputation gets diminished and they have to disclaim liability for the abuse, or waste their time sorting out misdirected bounce messages.
You probably have experienced one kind of abuse or another of your e-mail address yourself in the past, e.g. when you received an error message saying that a message allegedly sent by you could not be delivered to the recipient, although you never sent a message to that address.
Sender address forgery is a threat to users and companies alike, and it even undermines the
e-mail medium as a whole because it erodes people's confidence in its reliability. That is why your bank never sends you information about your account by e-mail and keeps making a point of that fact.
But it does not have to be this way!
The Solution: SPF
The
Sender Policy Framework (SPF) is an
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید] specifying a technical method to prevent sender address forgery. More precisely, the
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید] — called
SPFv1 or
SPF Classic — protects the
envelope sender address, which is used for the delivery of messages. See the box on the right for a quick explanation of the different types of sender addresses in e-mails.
(There are
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید] that protect the
header sender address or that do not care at all about who sent the message, only who originally wrote it.)
Even more precisely,
SPFv1 allows the owner of a domain to specify their mail sending policy, e.g. which mail servers they use to send mail from their domain. The technology requires two sides to play together:
(1) the domain owner publishes this information in an
SPF record in the domain's
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید] [فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید], and when someone else's mail server receives a message claiming to come from that domain, then
(2) the receiving server can check whether the message complies with the domain's stated policy. If, e.g., the message comes from an unknown server, it can be considered a fake.
Once you are confident about the authenticity of the sender address, you can finally "take it for real" and attach reputation to it. While IP-address-based reputation systems like
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید] or
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید] have prevailed so far, reputation will increasingly be based on domains and even individual e-mail addresses in the future, too. Furthermore, additional kinds of policies are planned for a future version of
SPF, such as asserting that all of a domain's outgoing mail is
S/MIME or
PGP signed.
An Example Policy
Let's look at an example to give you an idea of how SPF works. Bob owns the domain example.net. He also sometimes sends mail through his GMail account. Since he often receives bounces about messages he didn't send, he decides to publish an SPF record in order to reduce the abuse of his domain in e-mail envelopes:example.net. TXT "v=spf1 mx a:pluto.example.net include:gmail.com -all"
The parts of the
SPF record mean the following:
v=spf1
SPF version 1mxthe incoming mail servers (MXes) of the domain are authorized to also send mail for example.neta:pluto.example.netthe machine pluto.example.net is authorized, tooinclude:gmail.comeverything considered legitimate by gmail.com is legitimate for example.net, too-allall other machines are
not authorized
This example demonstrates but a small part of
SPF's expressiveness. Do
not take it as a guideline for building your own record — things might not work out as you expect and legitimate messages might get blocked! Instead, learn more about the
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید], or get the complete picture by studying the
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید].
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید] is available.
Receiver-side Checking
The domain sender policies alone are not worth much — it is the receiving mail servers that need to enforce them. Most mail servers do not yet support
SPF checking natively, however there are
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید] for most open-source MTAs and many commercial ones. Again, you can get
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید].
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید] |
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید]
Last edited 2006-11-09 15:15 (UTC) by
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید] [فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید]
more info
[فقط اعضا می توانند لینک ها را مشاهده کنند برای ثبت نام اینجا را کلیک کنید]
Sender Policy Framework
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