Sender Policy Framework — Википедия

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Email spam and phishing often use forged 'from' addresses, so publishing and checking SPF records can be considered anti-spam techniques. The first public mention of the concept was in but went mostly unnoticed. Over the next six months, a large number of changes were made and a large community had started working on SPF. The Simple Mail Transfer Protocol permits any computer to send email claiming to be from any source address. This is exploited by spammers who often use forged email addresses , \\\\\\\\\\\\\[6\\\\\\\\\\\\\] making it more difficult to trace a message back to its source, and easy for spammers to hide their identity in order to avoid responsibility. It is also used in phishing techniques, where users can be duped into disclosing private information in response to an email purportedly sent by an organization such as a bank. SPF allows the owner of an Internet domain to specify which computers are authorized to send mail with envelope-from addresses in that domain, using Domain Name System DNS records. Receivers verifying the SPF information in TXT records may reject messages from unauthorized sources before receiving the body of the message. Current practice requires the use of TXT records, \\\\\\\\\\\\\[7\\\\\\\\\\\\\] just as early implementations did. The envelope-from address is transmitted at the beginning of the SMTP dialog. If the server rejects the domain, the unauthorized client should receive a rejection message, and if that client was a relaying message transfer agent MTA , a bounce message to the original envelope-from address may be generated. If the server accepts the domain, and subsequently also accepts the recipients and the body of the message, it should insert a Return-Path field in the message header in order to save the envelope-from address. While the address in the Return-Path often matches other originator addresses in the mail header such as the header-from , this is not necessarily the case, and SPF does not prevent forgery of these other addresses such as sender header. Spammers can send email with an SPF PASS result if they have an account in a domain with a sender policy, or abuse a compromised system in this domain. However, doing so makes the spammer easier to trace. They receive large numbers of unsolicited error messages and other auto-replies. If such receivers use SPF to specify their legitimate source IP addresses and indicate FAIL result for all other addresses, receivers checking SPF can reject forgeries, thus reducing or eliminating the amount of backscatter. SPF has potential advantages beyond helping identify unwanted mail. Scenarios like compromised systems and shared sending mailers limit this use. If a domain publishes an SPF record, spammers and phishers are less likely to forge emails pretending to be from that domain, because the forged emails are more likely to be caught in spam filters which check the SPF record. Therefore, an SPF-protected domain is less attractive to spammers and phishers. Because an SPF-protected domain is less attractive as a spoofed address, it is less likely to be blacklisted by spam filters and so ultimately the legitimate email from the domain is more likely to get through. SPF breaks plain message forwarding. They should test e. See below for a list of alternatives to plain message forwarding. It can also be used in reputation systems any white or black list is a simple case of a reputation system. The records laid out below are in typical DNS syntax:. The following words provide mechanisms to use to determine if a domain is eligible to send mail. The 'ip4' and 'a' 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. The modifiers allow for future extensions to the framework. To date only the two modifiers defined in the RFC have been widely deployed:. Skipping erroneous mechanisms cannot work as expected, therefore include: Another safeguard is the maximum of ten mechanisms querying DNS, i. This last query counts as the first mechanism towards the limit In , Steven M. Bellovin wrote an email discussing his concerns with SPF. SPF proponents readily acknowledge that it would be better to have records specifically designated for SPF, but this choice was made to enable rapid implementation of SPF. Later on, \\\\\\\\\\\\\[7\\\\\\\\\\\\\] the use of SPF records was discontinued, and as of \\\\\\\\\\\\\[update\\\\\\\\\\\\\] , it is still necessary to use TXT records. An independent draft was proposed later, documenting how the spurious recursion to TXT records is characterized in the current Internet. As SPF increasingly prevents spammers from spoofing the envelope-from address, many have moved to utilising the header-from address as seen by the recipient user rather than processed by the recipient MTA. Propitiatory implementation beyond the scope of the SPF schema are required to protect against certain header-from spoofing implementations. Anti-spam software such as SpamAssassin version 3. From Wikipedia, the free encyclopedia. First Public Mention '. Retrieved 28 August Retrieved 16 May Retrieved 16 December Retrieved 26 April Archived from the original on January 29, Moonesamy 23 April Retrieved 25 August Archived from the original on Retrieved from ' https: Email authentication Internet architecture Internet governance Internet protocols Network addressing Spam filtering. Pages using RFC magic links Articles containing potentially dated statements from All articles containing potentially dated statements. Views Read Edit View history. This page was last edited on 13 November , at By using this site, you agree to the Terms of Use and Privacy Policy. Matches always; used for a default result like -all for all IPs not matched by prior mechanisms. This mechanism is deprecated and should no longer be used. If the given domain name resolves to any address, match no matter the address it resolves to. This is rarely used. References the policy of another domain. However, if the included policy fails, processing continues.

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