- Version 1.0
Author: DataParadise <[email protected]>
This tutorial shows how to get DKIM working on a CentOS box running Postfix using OpenDKIM, I’ll also cover some simple trouble shooting tips and advice for future upgrade on your OpenDKIM installation.
This tutorial is part 1 of the mailserver set-up with virtual users and domains using Postfix and Dovecot series. It goes through the steps of installing and integrating OpenDKIM in Postfix on a CentOS 7 Linux VPS. After completing this tutorial you will end-up having OpenDKIM adding digital signatures to your emails, thus making the Mailserver set-up even more robust and professional.
What is Open DKIM?
It is a digital email signing/verification technology, which is already supported by some common mail providers. In general, DKIM means digitally signing all messages on the mail-server to verify the message was actually sent from the domain in question and was not spam
UPDATE THE SYSTEM
Before going any further, make sure you’re in a screen session and your system is fully up-to-date by running:
## screen -U -S open dkim-screen
## yum update
ENABLE EPEL REPOSITORY
Open DKIM is available in the EPEL repository, so we need to enable it on the system before we can install Open DKIM
## wget -P /tmp http://mirror.pnl.gov/epel/6/i386/epel-release-6-8.noarch.rpm
## rpm -Uvh /tmp/epel-release-6-8.noarch.rpm
## rm -f /tmp/epel-release-6-8.noarch.rpm
INSTALL OPENDKIM
Install the package using yum:
## yum install opendkim
CONFIGURE OPENDKIM
Next thing to do is to configure OpenDKIM. Its main configuration file is located in /etc/opendkim.conf, so before making any changes create a backup and add/edit the following:
## cp /etc/opendkim.conf{,.orig}
## vim /etc/opendkim.conf
AutoRestart Yes
AutoRestartRate 10/1h
LogWhy Yes
Syslog Yes
SyslogSuccess Yes
Mode sv
Canonicalization relaxed/simple
ExternalIgnoreList refile:/etc/opendkim/TrustedHosts
InternalHosts refile:/etc/opendkim/TrustedHosts
KeyTable refile:/etc/opendkim/KeyTable
SigningTable refile:/etc/opendkim/SigningTable
SignatureAlgorithm rsa-sha256
Socket inet:[email protected]
PidFile /var/run/opendkim/opendkim.pid
UMask 022
UserID opendkim:opendkim
TemporaryDirectory /var/tmp
SET-UP PUBLIC/PRIVATE KEYS
Generate set of keys for your mydomain.com domain name:
## mkdir /etc/opendkim/keys/mydomain.com ## opendkim-genkey -D /etc/opendkim/keys/mydomain.com/ -d mydomain.com -s default ## chown -R opendkim: /etc/opendkim/keys/mydomain.com ## mv /etc/opendkim/keys/mydomain.com/default.private /etc/opendkim/keys/mydomain.com/default addmydomain.comto OpenDKIM’s key table by adding the following record in/etc/opendkim/KeyTabledefault._domainkey.mydomain.com mydomain.com:default:/etc/opendkim/keys/mydomain.com/default
/etc/opendkim/SigningTable and add the following record to OpenDKIM’s signing table:
*@mydomain.com default._domainkey.mydomain.com
and add your domain and your hostname as trusted hosts in /etc/opendkim/TrustedHosts:
127.0.0.1 mydomain.com host.mydomain.com assuming the domain in question is ‘mydomain.com’ and server’s hostname is set to ‘host.mydomain.com’
finally, edit your mydomain.com DNS zone and add the TXT record from /etc/opendkim/keys/mydomain.com/default.txt
default._domainkey IN TXT ( "v=DKIM1; k=rsa; "
"p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDApHRr7ZmXRaAB+RQRbP4VdMwIrIHIP18KFtXRsv/xpWc0Gix6ZXN13fcG03KNGKZo2PY+csPkGC5quDnH5V0JEhDZ78KcDWFsU6u4fr9ktVAdt6P7jWXjcyqdHOZ8+YN4cAeU4lRFNgQvdupIcByYwzPYMgBFHfJm9014HvRqhwIDAQAB" ) ; ----- DKIM key default for mydomain.com
it is also a good idea to add an SPF record if you haven’t already
mydomain.com. 14400 IN TXT "v=spf1 a mx ~all"
you can verify your dkim TXT record is valid using dig for example:
## dig +short default._domainkey.mydomain.com TXT
"v=DKIM1\; k=rsa\; " "p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDApHRr7ZmXRaAB+RQRbP4VdMwIrIHIP18KFtXRsv/xpWc0Gix6ZXN13fcG03KNGKZo2PY+csPkGC5quDnH5V0JEhDZ78KcDWFsU6u4fr9ktVAdt6P7jWXjcyqdHOZ8+YN4cAeU4lRFNgQvdupIcByYwzPYMgBFHfJm9014HvRqhwIDAQAB"
CONFIGURE POSTFIX
In order to integrate OpenDKIM with Postfix we need to add the following few lines in /etc/postfix/main.cf:
smtpd_milters = inet:127.0.0.1:8891
non_smtpd_milters = $smtpd_milters
milter_default_action = accept
milter_protocol = 2
(RE)START SERVICES
Add OpenDKIM to your system’s start-up and start opendkim and restart postfix using the following commands:
## service opendkim start
## chkconfig opendkim on
## service postfix restart
TEST THE SET-UP
To test the set-up simply send an email to
[email protected] and you should receive back an email containing something like this:
==========================================================
Summary of Results
==========================================================
SPF check: pass
DomainKeys check: neutral
DKIM check: pass
DKIM check: pass
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