Hi,

Please note that :

    This is the revision 2 of this Work In Progress How-To
    Until this is natively integrated in YnH core apps, it will mean to that postfix conf will be blocked (or each time there is a change some configuration lines will need to be added to the end of /etc/postfix/main.cf)
    To be fully functionnal DKIM requires a modification of the DNS, which propagantion can take up to 24h
    CREDIT : This tutorial has been initially based on the DKMI section of : http://sealedabstract.com/code/nsa-proof-your-e-mail-in-2-hours/ from Drew Crawford
    CREDIT : This tutorial has been reviewed based on https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-dkim-with-postfix-on-debian-wheezy from Popute Sebastian Armin
    Replace DOMAIN.TLD by your own domain name

Changes in rev 2 :

    Much easier to manage more than one DOMAIN.TLD (future proof)
    Updated configuration as it seemed that the previous one was based on old software

So, here is the thing :

    We start by installing the right software : 

sudo aptitude install opendkim opendkim-tools

    Then we configure opendkim 

sudo nano /etc/opendkim.conf
(Text to be placed in the text file: )

AutoRestart Yes
AutoRestartRate 10/1h
UMask 022
Syslog yes
SyslogSuccess Yes
LogWhy Yes

Canonicalization relaxed/simple

ExternalIgnoreList refile:/etc/opendkim/TrustedHosts
InternalHosts refile:/etc/opendkim/TrustedHosts
KeyTable refile:/etc/opendkim/KeyTable
SigningTable refile:/etc/opendkim/SigningTable

Mode sv
PidFile /var/run/opendkim/opendkim.pid
SignatureAlgorithm rsa-sha256

UserID opendkim:opendkim

Socket inet:8891@127.0.0.1

Selector mail

    Connect the milter to Postfix:

sudo nano /etc/default/opendkim

(Text to be placed in the text file: )
SOCKET="inet:8891@localhost"

    Configure postfix to use this milter:

sudo nano /etc/postfix/main.cf

(Text to be placed AT THE END in the text file: )
milter_protocol = 2
milter_default_action = accept
smtpd_milters = inet:127.0.0.1:8891
non_smtpd_milters = inet:127.0.0.1:8891

    Create a directory structure that will hold the trusted hosts, key tables, signing tables and crypto keys:

sudo mkdir -pv /etc/opendkim/keys/DOMAIN.TLD

    Specify trusted hosts:

sudo nano /etc/opendkim/TrustedHosts

(Text to be placed in the text file: )
127.0.0.1
localhost
192.168.0.1/24
*.DOMAIN.TLD

    Create a key table:

sudo nano /etc/opendkim/KeyTable

(Text to be placed in the text file: Be very careful, it needs to be on a SINGLE LINE for each domain )
mail._domainkey.DOMAIN.TLD DOMAIN.TLD:mail:/etc/opendkim/keys/DOMAIN.TLD/mail.private

    Create a signing table:

sudo nano /etc/opendkim/SigningTable

(Text to be placed in the text file: )
*@DOMAIN.TLD mail._domainkey.DOMAIN.TLD

    Now we generate the keys ! smile 

sudo cd /etc/opendkim/keys/DOMAIN.TLD
sudo opendkim-genkey -s mail -d DOMAIN.TLD

    Output the DKIM DNS line to the terminal. Then, we install it on our DNS server. My ZONE file looks like this. (Be very careful with the formatting, the "p=...." needs to be in a single line.

cat mail.txt

mail._domainkey IN TXT "v=DKIM1; k=rsa; p=AAAKKUHGCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDPFrBM54eXlZPXLJ7EFphiA8qGAcgu4lWuzhzxDDcIHcnA/fdklG2gol1B4r27p87rExxz9hZehJclaiqlaD8otWt8r/UdrAUYNLKNBFGHJ875467jstoAQAB" ; ----- DKIM key mail for DOMAIN.TLD

    And we don't forget to put the right rights otherwise opendkim will get grumpy...

chown -Rv opendkim:opendkim /etc/opendkim*

    And finally, we restart everything :
    sudo service opendkim restart
    sudo service postfix restart

    To test if it is all working well (don't forget that the DNS propagation can take a bit of take....) you can simply send an email to check-auth@verifier.port25.com and a reply will be received. If everything works correctly you should see DKIM check: pass under Summary of Results.