apt-get install opendkim opendkim-tools
mkdir -p /etc/dkim
opendkim-genkey -D /etc/dkim/ -d lebonfilon.fr -s mail

chown opendkim:opendkim -R /etc/dkim

vi /etc/opendkim.conf UserID opendkim:opendkim Domain votreDomaine.net KeyFile /etc/dkim/mail.private Selector mail AutoRestart yes DNSTimeout 5

vi /etc/default/opendkim
SOCKET="inet:8891:localhost"

vi /etc/postfix/main.cf :
# DKIM milter_default_action = accept
milter_protocol = 2
smtpd_milters = inet:localhost:8891
non_smtpd_milters = inet:localhost:8891

service opendkim restart service postfix restart

mettre contenu du mail.txt dans la zone dns