Installing OpenDKIM on Linux and connectcing to Postfix for multiple domains
apt-get install opendkim emerge -av opendkim USE="berkdb gnutls -ldap -lua -opendbx -poll sasl ssl -static-libs -unbound" yum install opendkim
Configuring OpenDKIM
OpenDKIM is super simple to get configured.
The entire configuration is stored in files in /etc/opendkim, starting with opendkim.conf
LogWhy Yes Syslog yes SyslogSuccess yes Socket inet:8891@localhost ReportAddress root@domain.tld SendReports yes UserID milter PidFile /var/run/opendkim/opendkim.pid Mode s Canonicalizatio relaxed/simple Statistics /var/lib/opendkim/stats.dat Domain domain.tld KeyFile /etc/opendkim/domain.tld.key Selector mail ExternalIgnoreList file:/etc/opendkim/TrustedHostList.txt InternalHosts file:/etc/opendkim/TrustedHostList.txt # KeyFile /etc/opendkim/KeyFile.txt
Generate Keys
opendkim-genkey --domain=example.com --selector=mail --verbose
This will produce two files named mail.private and mail.txt.
Rename them to something more meaningfull.
mv mail.private example.com.key mv mail.txt example.com.dns
Update the DNS
Once you have the keys from the above command you'll need to update the DNS. The value of the TXT record should be this, the host part is using $selector._domainkey. The Key Data will be a very long string of Base64 encoded bits.
mail._domainkey TXT v=DKIM1; k=rsa; p=[Key Data Here]
Once this is entered, you'l want to want to wait a bit for the DNS system to catch up.
Trusted Hosts
Create a file of hosts that DKIM should trust, one per line and comments are allowed. Here are example contents for our domain.
# # External Hosts that OpenDKIM will Trust edoceo.com gcdn.org he.edoceo.com s001.edoceo.com
Multiple Domains
KeyFile: /etc/opendkim/KeyFile.txt
# $sender-pattern:$signing-domain:$keypath *@domainA.com:domainA.com:/etc/opendkim/domainA.com.key *@domainB.com:domainB.com:/etc/opendkim/domainB.com.key *@domainC.com:domainC.com:/etc/opendkim/domainC.com.key
Update Signing Table
*@domainA.com mail._domainkey.domainA.com *@domainB.com mail._domainkey.domainB.com
Connecting Postfix
Update main.cf to point to the OpenDKIM service.
# # Add the DKIM milter milter_default_action = accept milter_protocol = 2 smtpd_milters = inet:localhost:8891 non_smtpd_milters = inet:localhost:8891