page_title: Email authentication
section_title: SPF
hierarchical_section_title: Email authentication / Authentication methods in widespread use / SPF
caption_attribution_description: English: SPF authenticates the sender address by querying the Domain Name System for labels found in the message envelope of an email message.
context_page_description: Email authentication, or validation, is a collection of techniques aimed at providing verifiable information about the origin of email messages by validating the domain ownership of any message transfer agents who participated in transferring and possibly modifying a message.
  The original base of Internet email, Simple Mail Transfer Protocol, has no such feature, so forged sender addresses in emails have been widely used in phishing, email spam, and various types of fraud. To combat this, many competing email authentication proposals have been developed, but only fairly recently have three been widely adopted – SPF, DKIM and DMARC. The results of such validation can be used in automated email filtering, or can assist recipients when selecting an appropriate action.
context_section_description: SPF allows the receiver to check that an email claimed to have come from a specific domain comes from an IP address authorized by that domain's administrators. Usually, a domain administrator will authorize the IP addresses used by their own outbound MTAs, including any proxy or smarthost.
  The IP address of the sending MTA is guaranteed to be valid by the Transmission Control Protocol, as it establishes the connection by checking that the remote host is reachable.  The receiving mail server receives the HELO SMTP command soon after the connection is set up, and a Mail from: at the beginning of each message.  Both of them can contain a domain name.  The SPF verifier queries the Domain Name System (DNS) for a matching SPF record, which if it exists will specify the IP addresses authorized by that domain's administrator. The result can be "pass", "fail", or some intermediate result - and systems will generally take this into account in their anti-spam filtering.
caption: SPF authenticates the sender IP address.
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