<Li> Received: when an SMTP server accepts a message it inserts this trace record at the top of the header (last to first). </Li> <Li> Return - Path: when the delivery SMTP server makes the final delivery of a message, it inserts this field at the top of the header . </Li> <P> Other fields that are added on top of the header by the receiving server may be called trace fields, in a broader sense . </P> <Ul> <Li> Authentication - Results: when a server carries out authentication checks, it can save the results in this field for consumption by downstream agents . </Li> <Li> Received - SPF: stores results of SPF checks in more detail than Authentication - Results . </Li> <Li> Auto - Submitted: is used to mark automatically generated messages . </Li> <Li> VBR - Info: claims VBR whitelisting </Li> </Ul>

When was email made available to the public