s/qmail/DOC/5について、ここに記述してください。
5. Authentication & Authorization
http://fehcom.de/sqmail/sqmaildoc_05.html
5.5.1 Additional qmail-smtpd settings
qmail-smtpd includes the authentication information in the the Received: header and displays the provided Distinguished Name of the user identity. The DN should include the email address of the sender.
In general, there is no connection between the DN and the ESMTP 'Return-Path' address, but this can enforced. For this purpose, the environment variable LOCALMFCHECK="?" can be set; typically as provided in the cdb. Now, only ESMTPA connections with matching conditions are granted.
5.10 SPF Records and Domain Authorization