Basic E-mail Authentication Flow

By Ellen Siegel  |  Posted 2009-03-30 Print this article Print

Basic e-mail authentication flow

The basic e-mail authentication flow is the same for both Sender ID and DKIM, with some minor differences in Steps 2, 3 and 4:

Step No. 1: The author composes a message and hits Send, which causes the message to be transmitted from the mail client to the sending mail server.

Step No. 2: The sending mail server identifies the recipient, processes the message, performs any necessary authentication, constructs the message headers and sends the message to the recipient's mail server.

Step No. 3: The receiving mail server processes the incoming message. It then queries the sender's DNS entry for any relevant authentication information.

Step No. 4: The receiving mail server uses the authentication information to validate the incoming message.

Step No. 5: The receiver's back-end processing combines the results of the authentication with any relevant reputation data and content filtering to determine whether the message will be delivered to the recipient's inbox, junk folder or whether it will be blocked completely.

Step No. 6: Finally, the recipient will be able to access the message the next time e-mail status is updated, assuming it has not been blocked.

Ellen Siegel is Director of Technology and Standards at Constant Contact. With more than 20 years of experience in online communication technologies, Ellen works to define and drive the adoption of industry best practices and standards to help fight spam, support legitimate e-mail, and enable Constant Contact to serve the growing needs of small businesses and organizations. Ellen is a board member and technical committee co-chair for the E-mail Sender and Provider Coalition (ESPC) and an active member of the Messaging Anti-Abuse Working Group (MAAWG). She can be reached at

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