The email message header contains information that enables the authentication of the email address.

4 fields that are maintained in the header:

X-New-Auth-Key

This key is sent periodically from the Authentication Server in the header of a new message. It contains the new Authentication Key.

X-Auth-Key

This is the sender email address Authentication Key that the SMTP Server or the Mail Client attaches to the message header. The key is a string that the Authentication Server generates its value.

The Recipient SMTP Server uses this value with the sender email address to authenticate the email address.

The Recipient SMTP server removes the key from the header.

X-Auth-Agent

This field provides the information of who put the Authentication Key in the header. The type, SMTP or mail Client and the brand. This field is being used for debugging purposes.

X-Auth-Key-Status

The Recipient SMTP Server should verify that other SMTP Server does not place the field already. If the key is already there it should be removed to avoid forging the X-Auth-Key-Status.

The Recipient SMTP Server can put the value of the authentication in this field for further processing by the mail delivery agent or/and by the mail client.

The Recipient SMTP Server should verify that the field is not placed already by other SMTP Servers.