Process

Enable the EPEL yum
Install dkim-milter
```
sudo yum install dkim-milter
```

Generate keys

dkim-genkey -r -d example.com
sudo mkdir /etc/mail/dkim-milter/keys/example.com
sudo mv default.private /etc/mail/dkim-milter/keys/example.com/default
sudo mv default.txt /etc/mail/dkim-milter/keys/example.com/
sudo chown -R dkim-milter:dkim-milter /etc/mail/dkim-milter/keys/example.com

Paste the contents of default.txt into your zone file

cat /etc/mail/dkim-milter/keys/example.com/default.txt >> /var/named/chroot/var/named/example.com.hosts

Modify your zone file’s serial number to reflect that fact that you’ve changed it. This is necessary for the changes to be propogated
Change settings in /etc/mail/dkim-milter/dkim-filter.conf.orig
- AutoRestart yes
- Domain example.com
- Selector default
- Socket inet:20209@localhost
- Syslog Yes
- X-Header Yes

Modify /etc/mail/dkim-milter/keys/keylist

*@example.com:example.com:/etc/mail/dkim-milter/keys/example.com/default

Modify /etc/postfix/main.cf

# dkim-milter setup
smtpd_milters = inet:localhost:20209
non_smtpd_milters = inet:localhost:20209
milter_protocol = 2
milter_default_action = accept

Tell dkim-filter to listen on a port instead of a socket. This is required because the init script hard codes to a socket and doesn’t respect the setting in the /etc/mail/dkim-milter/dkim-milter.conf file.
```
sudo echo "SOCKET=inet:20209@localhost" >>/etc/sysconfig/dkim-milter
```

Start it up

sudo service dkim-milter start
sudo service postfix restart
sudo service named reload

Test it out