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Sender ID Verify

The Sender ID Framework is an e-mail authentication technology protocol that helps address the problem of spoofing and phishing by verifying the domain name from which e-mail messages are sent. Sender ID validates the origin of e-mail messages by verifying the IP address of the sender against the alleged owner of the sending domain. Now adopted by more than 10 million domains worldwide, Sender ID is providing brand owners, senders, and receiving networks with significant business and technical value.


How Sender ID Works

Sender ID seeks to verify that every e-mail message originates from the Internet domain from which it claims to have been sent. This is accomplished by checking the address of the server that sent the mail against a registered list of servers that the domain owner has authorized to send e-mail. This verification is automatically performed by the Internet service provider (ISP) or the recipient's mail server before the e-mail message is delivered. The result of the Sender ID check can be incorporated into the filtering tasks that are already performed by the mail server. After the sender has been authenticated, the mail server may apply conventional content filters and consider past behaviors, traffic patterns, and sender reputation when determining whether to deliver mail to the recipient.

To use SIDF, e-mail senders and domain owners must publish or declare all of the Internet Protocol (IP) addresses used by their outbound e-mail servers, or the IPs authorized to send e-mail on their behalf, in the Domain Name System (DNS). These IPs are included in a Sender Policy Framework (SPF) text file.

The following diagram and steps outline the SIDF process:


A sender or user sends an e-mail message from an e-mail client or Web interface. No interaction or changes to the sender's client or Mail Transfer Agent (MTA) are required.


The recipient's inbound e-mail server receives the e-mail message. The server uses SIDF and calls the Purported Responsible Domain's (PRA) DNS for the SPF(Sender Policy Framework ) record.


The receiving MTA determines whether the outbound e-mail server's IP address matches the IP addresses that are authorized to send e-mail for the domain.


For most domains and IPs, sender reputation data is applied to the SIDF verdict check.


Based on the SPF record syntax, the pass or fail verdict, the reputation data, and the content filtering score, the receiving MTA delivers the e-mail message to the inbox, a junk or bulk folder, or a quarantine folder. If an e-mail message fails, the receiving network may block, delete, or junk the e-mail.

A Significant Step Forward

There is no single solution that will stop all spam and online fraud. However, Sender ID is a significant step, and more than 12 million domains worldwide are using it as a means to counter spam and online phishing attacks. Other complementary technologies are also being developed and will coexist with Sender ID. These include signing solutions and additional antispam filters, such as Microsoft SmartScreen, which works with MSN, Windows Live Hotmail, Microsoft Office Outlook, and Microsoft Exchange Server.


How Sender ID Works

Domain administrators publish Sender of Policy Framework (SPF) records in the Domain Name System (DNS) which identify authorized outbound e-mail servers. Receiving e-mail systems verify whether messages originate from properly authorized outbound e-mail servers. The following diagram illustrates the verification process.

Four steps in the Sender ID e-mail verification process.

Sender ID at work. Only authenticated messages are allowed to reach the receiver.


The steps in the process are:


The sender transmits an e-mail message to the receiver.


The receiver's inbound mail server receives the mail.


The inbound server checks which domain claims to have sent the message, and checks the DNS for the SPF record of that domain. The inbound server determines if the sending e-mail server's IP address matches any of the IP addresses that are published in the SPF record.


If the IP addresses match, the mail is authenticated and delivered to the receiver. If the addresses do not match, the mail fails authentication and is not delivered.