Follow these steps to install OpenDKIM on Ubuntu and Plesk.
I will use domain.tld (as the primary domain) and example.com as my domains, I have enabled subdomains so mail from the server mail.domain.tld gets signed too as in this case mail.domain.tld is also the Posfix hostname and mailname…
1. First login as root as run…
# apt-get update
# apt-get install opendkim opendkim-tools
2. Create the folder structure…
# mkdir -p /etc/opendkim/keys/domain.tld
# mkdir -p /etc/opendkim/keys/example.com
3. Create a key, I’ll use “dkim” as the selector and create 1024bit keys
You will have two files in the folder, dkim.private and dkim.txt, the latter contains the DNS record for you to add in Plesk or at your domains registrar.
# cd /etc/opendkim/keys/domain.tld
# opendkim-genkey -s dkim -d domain.tld
# chown opendkim:opendkim dkim.private
# chmod 600 dkim.private
And example.com…
# cd /etc/opendkim/keys/example.com
# opendkim-genkey -s dkim -d example.com
# chown opendkim:opendkim dkim.private
# chmod 600 dkim.private
4. Now we’ll create the SigningTable and the KeyTable…
# nano /etc/opendkim/SigningTable
The contents should look like…
domain.tld dkim._domainkey.domain.tld
mail.domain.tld dkim._domainkey.domain.tld
example.com dkim._domainkey.example.com
mail.example.com dkim._domainkey.example.com
5. And the KeyTable…
# nano /etc/opendkim/KeyTable
The contents should look like…
dkim._domainkey.domain.tld domain.tld:dkim:/etc/opendkim/keys/domain.tld/dkim.private
dkim._domainkey.domain.tld mail.domain.tld:dkim:/etc/opendkim/keys/domain.tld/dkim.private
dkim._domainkey.example.com example.com:dkim:/etc/opendkim/keys/example.com/dkim.private
dkim._domainkey.example.com mail.example.com:dkim:/etc/opendkim/keys/example.com/dkim.private
You can see the subdomains point to the same key as the domain.
6. Next we have to create the internal hosts file…
# nano /etc/opendkim/dkim-InternalHosts
and add your IP and host names…
127.0.0.1/8
192.168.0.50/32 # where this is your Server IP
localhost
domain.tld
mail.domain.tld
example.com
mail.example.com
7. Now edit /etc/opendkim.conf
# nano /etc/opendkim.conf
And define these settings…
Syslog yes
UMask 002
Domain domain.tld
KeyFile /etc/opendkim/keys/domain.tld/dkim.private
Selector dkim
Canonicalization relaxed/relaxed
Mode sv
SignatureAlgorithm rsa-sha256
SubDomains yes
LogWhy yes
UserID opendkim:opendkim
KeyTable /etc/opendkim/KeyTable
SigningTable /etc/opendkim/SigningTable
InternalHosts /etc/opendkim/dkim-InternalHosts
Statistics /var/log/opendkim/dkim-stats.log
OversignHeaders From
8. Make sure you create the log directory, and the log file is owned by opendkim:opendkim
# mkdir -p /var/log/opendkim/
# touch /var/log/opendkim/dkim-stats.log
# chown opendkim:opendkim /var/log/opendkim/dkim-stats.log
9. We now need to define the socket…
# nano /etc/default/opendkim
And uncomment…
SOCKET="inet:12345@localhost" # listen on loopback on port 12345
10. And restart opendkim
# service opendkim restart
11. Our last step is too add this milter to our postfix configuration file…
# nano /etc/postfix/main.cf
milter_default_action = accept
milter_protocol = 6
smtpd_milters = inet:127.0.0.1:12768, inet:127.0.0.1:12345
non_smtpd_milters = inet:127.0.0.1:12345
Restart Postfix…
# service postfix restart
And you should be good.