Install OpenDKIM with Postfix on CentOS

Install opendkim    ( epel repoor other sources )

Either find/add those options to the original config file, or even better, make a copy of the original file and replace /etc/opendkim.conf with the following:

AutoRestart             Yes      # Need to investigate this option !!!
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
Selector                   mail
SignatureAlgorithm      rsa-sha256
Socket                  inet:8891@localhost
PidFile                 /var/run/opendkim/opendkim.pid
UMask                   022
UserID                  opendkim:opendkim
TemporaryDirectory      /var/tmp

Now we have to setup the public and private keys (replace yourdomain in the text with the apropriate domain name):

mkdir /etc/opendkim/keys/yourdomain
opendkim-genkey -D /etc/opendkim/keys/yourdomain/ -d yourdomain -s mail
chown -R opendkim: /etc/opendkim/keys/yourdomain
mv /etc/opendkim/keys/yourdomain/mail.private /etc/opendkim/keys/yourdomain/mail

Now we have to add it to the OpenDKIM keytable. Edit /etc/opendkim/KeyTable and add:

mail._domainkey.yourdomain yourdomain:mail:/etc/opendkim/keys/yourdomain/mail

Next step, adding the domain to the signing table. Edit /etc/opendkim/SigningTable, and insert:

*@mydomain.com mail._domainkey.mydomain.com

And the last move with DKIM, edit /etc/opendkim/TrustedHosts and add your LAN there.

Now we have to tell Postfix that we want to use OpenDKIM miltering. Edit /etc/postfix/main.cf and insert at the end of the file:

smtpd_milters = , inet:127.0.0.1:12768, inet:127.0.0.1:8891
non_smtpd_milters       = $smtpd_milters
milter_default_action   = accept
milter_protocol         = 6

The port 12768 is used by amavisd-new in this case !!!

Now we can try to start OpenDKIM and reload postfix:

service opendkim start
chkconfig opendkim on
service postfix reload

If everything worked well, You can send a test mail and see in the source and it contains a DKIM signature, tail /var/log/maillog -f and see the OpenDKIM entries like DKIM-Signature field added (s=mail, d=yourdomain)

Now you should add the dkim signature to your domain file (probably at your ISP). The exact signature as it should look was generated by the opendkim certificate generator, and it is located in /etc/opendkim/keys/yourdomain/mail.txt

TXT record – mail._domainkey

v=DKIM1; k=rsa; p=MIGfM………….

So, all you need is to insert it in the DNS zone file or send it to Your ISP if the DNS is hosted and after a while it will start to work. If you want to check if the DKIM signature is properly inserted in your DNS zone, you can do dig +short mail._domainkey.yourdomain TXT
and it should give You and answer with the hashed key.

Hint:
After a working OpenDKIM and SPF, you might want to join it together with the new DMARC technology!

 

SOURCE: https://www.prosinger.net/opendkim-postfix/

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