Sender Policy Framework (SPF): An Email Authentication Technique

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Sender Policy Framework (SPF) An Email
Authentication Technique
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Table of Contents

• Sender Policy Framework (SPF)
• Email Authentication
• The Way Email Authentication Works

• Standards of Email Authentication
• Compliance with SPF
• Limitations of SPF

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Sender Policy Framework (SPF)

• SPF refers to a technique that is related to
  email-authentication. It has been designed to
  prevent spammers from using ones domain to send
  messages. SPF aids an enterprise in publishing
  authorized mail servers. This along with the
  information related to DMARC, equips the
  receiving system with information regarding the
  trustworthiness of an emails origin. It is only
  in combination with DMARC that SPF can come in
  handy for the detection of any forge related to
  the visible sender of an email.
• SPF lets the recipient mail server verify, at the
  time of the delivery of the mail, that an email
  which claims to have originated from a specific
  domain has been submitted by an IP address that
  is authorized by the administrators of that
  domain. Authorized sending hosts and IP
  addresses list for a domain are published and
  contained in the DNS records that are related to
  that domain.

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Email Authentication

• Email authentication refers to a collection of
  standardized techniques that provide verifiable
  information related to an email messages origin.
  It is an effective solution that helps to prove
  that an email is not forged and ascertains that
  the email has been sent by the very sender from
  whom it claims to have originated.
• Email authentication is used very frequently to
  prohibit harmful and/or fraudulent email
  practices.
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The Way Email Authentication
Works

• There are various ways in which email
  authentication works. Here, information is being
  provided on the general approach that is
  followed. A policy is established by an
  enterprise that sends emails. This policy
  specifies the rules that will authenticate emails
  from the enterprises domain name. The mail
  servers and other technical infrastructure of the
  email sender are configured accordingly to
  publish and implement these rules. When the mail
  server receives an email, it authenticates the
  received message by comparing details of the
  incoming email message with the rules that have
  been predefined. The result of this
  authentication check decides how the receiving
  mail server acts, which can either be the
  delivery of the message or its rejection or even
  flagging of the message.

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Standards of Email Authentication

• Email authentication relies on certain
  standardized technical solutions. These standards
  for email authentication are DKIM (DomainKeys
  Identified Mail), SPF (Sender Policy Framework)
  and DMARC (Domain-based Message Authentication,
  Reporting and Conformance).
• To mention these briefly, an encryption key and a
  digital signature are provided by DKIM to verify
  the authenticity of an email message and
  ascertain that it was neither fake nor altered.
  SPF lets senders define the IP addresses that are
  allowed to send mail for a particular domain. It
  is DMARC that unites the two above-mentioned
  authentication mechanisms (DKIM and SPF) into a
  common framework. It enables domain owners to
  specify the way in which an email will be handled
  which is from that domain and has failed an
  authorization test.

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Compliance with SPF

• Compliance with SPF entails the following tasks
• Publishing a Policy
• Those machines are identified by the domains and
  hosts that are authorized to send mail. This is
  accomplished by adding additional records to the
  DNS information that exists. Every host or domain
  name which has an A record or MX record should
  have an SPF record. If a policy is used, it is
  this SPF record that specifies the policy either
  in the address of an email or as HELO/EHLO
  argument.
• Checking and using SPF Information
• The SPF information is interpreted by the
  receivers, as per the specifications. Next, the
  receivers act on the result.
• Revising Mail Forwarding
• Since SPF doesnt allow plain mail forwarding,
  there are alternatives to it. These are mentioned
  below-
• Remailing- In it the original sender is replaced
  with one that belongs to the local domain.
• Refusing.
• Allow listing on the target server- This ensures
  that a forwarded message will not be refused.
• Sender Rewriting Scheme- This is a complicated
  mechanism. It handles the routing of non-delivery
  notifications to the original sender.

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Limitations of SPF

• Despite being an effective technique that adds
  authentication to emails, SPF has certain
  limitations. There has to be awareness about
  these limitations as well. These are mentioned
  below, in no particular order-
• The From header is not validated by SPF. It is
  shown in most clients and appears as the actual
  sender of a message. The header from is not
  validated by SPF. It uses the envelope from to
  ascertain the sending domain.
• In the event that an email is forwarded, SPF will
  break. At this juncture it is the forwarder
  that assumes the role of the new sender of the
  message. This fails the SPF checks that are
  performed by the new destination.
• A lack of reporting with regard to SPF, renders
  maintaining it difficult.

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