I am planning on implementing the three following How-To's that are found on this site. http://www.howtoforge.com/postfix_spf http://www.howtoforge.com/how-to-implement-domainkeys-in-postfix-using-dk-milter-centos5.1 http://www.howtoforge.com/postfix-dkim-with-dkim-milter-centos5.1 I am running Postfix on an Ubuntu 8.04 server which was setup to use a MySQL database for virtual users. It was configured by following this How-To http://www.howtoforge.com/virtual-users-domains-postfix-courier-mysql-squirrelmail-ubuntu8.04 As I understand, these methods require changes to DNS records. Where I am confused in in regards to which DNS records I need to add these TXT records. Do I only add the information for the DNS record of the email server? Or do I need to add a TXT record for each domain that is authorized to send mail through my email server? To me, the first one makes more sense since the email server is sending mail on behalf of the virtual host domains, but I am not sure I am correct in this thinking. Thanks.