FYI, This is a bug in a third-party IPv6 patch that is not part of Postfix. Neither the official Postfix release, nor the work-in-progress version are not affected by this. Wietse Martin Pitt: > Jean-Samuel Reynaud noticed a programming error in the IPv6 handling > code of Postfix when /proc/net/if_inet6 is not available (which is the > case in Ubuntu since Postfix runs in a chroot). If "permit_mx_backup" > was enabled in the "smtpd_recipient_restrictions", Postfix turned into > an open relay, i. e. erroneously permitted the delivery of arbitrary > mail to any MX host which has an IPv6 address.
