implement per-domain mail relaying

install/dist/lib/fedora.lib.php

install/dist/lib/gentoo.lib.php

install/dist/lib/opensuse.lib.php

install/lib/installer_base.lib.php

install/sql/incremental/upd_dev_collection.sql

install/sql/ispconfig3.sql

install/tpl/debian_postfix.conf.master

install/tpl/fedora_postfix.conf.master

install/tpl/gentoo_postfix.conf.master

install/tpl/mysql-virtual_sender-relayauth.cf.master

install/tpl/mysql-virtual_sender-relayhost.cf.master

install/tpl/opensuse_postfix.conf.master

interface/web/mail/form/mail_domain.tform.php

interface/web/mail/lib/lang/ar_mail_domain.lng

interface/web/mail/lib/lang/bg_mail_domain.lng

interface/web/mail/lib/lang/br_mail_domain.lng

interface/web/mail/lib/lang/ca_mail_domain.lng

interface/web/mail/lib/lang/cz_mail_domain.lng

interface/web/mail/lib/lang/de_mail_domain.lng

interface/web/mail/lib/lang/dk_mail_domain.lng