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How does SPF work?

It adds information in a domain's DNS record indicating which machines may legitimately send email for that domain. Domain must identify the machines that are authorized to send email on their behalf.
When mail server recieves email, they can check which computers are authorized to send mail for the domain of the email address in the From: field, and see if this message actually came from one of those authorized computers. If it did, the message is assumed to be legitimate and allowed through. If it did not, or if it is questionable, the receiving mail server can accept the message, mark it and accept it, or refuse to receive it.
For example: Suppose xyzzx.com receives mail at 198.0.2.1 and 198.0.2.2. When it sends mail, it uses those two servers, as well as 198.0.2.3. xyzzx.com would publish an SPF record that said: "v=spf1 ip4:198.0.2.1 ip4:198.0.2.2 ip4:198.0.2.3 -all".
When a mail server gets mail that claims to be from someone at xyzzx.com, that server can fetch xyzzx.com's SPF record and see if the connecting SMTP client is designated.

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Limitations

  • It doesn't do much to prevent the growing trend of spam sent from hijacked computers and spammers. They can still send emails from their domains.
  • Incompatibility of SPF with some email forwarding services and websites that use mail-forwarding features.
  • SPF may be hacked by the spammers before it is fully implemented.

At present the domains having published records are AOL, Amazon, Google, O'Reilly, SAP, TicketMaster,Mail. com, w3.org, Earthlink and Verizon etc.

Sender ID frame work

Sender ID frame work is the result of Microsoft's Caller ID for E-Mail proposal, Meng Wong's Sender Policy Framework (SPF), and a third specification called the Submitter Optimization. However, the Internet Engineering Task Force (IETF) has provisionally rejected Sender ID.
The Sender ID Framework is tasked with verifying that each e-mail message originates from the Internet domain from which it claims to come based on the sender's server IP address. Only authenticated messages are allowed to reach the Receiver.
  • The steps in the process are:
  • The Sender sends an e-mail message to the Receiver.
  • The Receiver's inbound mail server receives the mail.
  • The Receiver's server checks for the SPF record of the sending domain published in the Domain Name System (DNS) record.
  • The inbound e-mail server determines if the sending e-mail server's IP address matches the IP address that is published in the DNS record.

However, The Internet Engineering Task Force (IETF) has provisionally rejected Sender ID because of a possible intellectual property rights conflict. It was said that it should not be made a mandatory part of Marid (MTA Authorization Records in DNS) eventual standard.

Caller ID

Microsoft's Caller ID allows Internet domain owners to publish the IP address of their outgoing e-mail servers in an XML (Extensible Markup Language) format e-mail "policy" in the DNS record for their domain. E-mail servers can query the DNS record and match the source IP address of incoming e-mail messages to the address of the approved sending servers.
Caller ID involves two key steps:
One, sender of e-mail publishes the IP [Internet Protocol] addresses of their outgoing mail servers in DNS [Domain Name System] in an e-mail policy document.
Two, the e-mail software at the receiving end of a message queries DNS for the e-mail policy and determines the "purported responsible domain" of the message. This is done by comparing the information in DNS to ensure it matches the information on the originating mail. Caller ID claims to confirm legitimate senders.

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