Certificate

Source: Manuel Mausz' Perl script

1. DKIM sign all email with global key

 # yum install perl-XML-Simple perl-Mail-DKIM perl-XML-Parser
 # wget https://raw.githubusercontent.com/qmtoaster/dkim/master/qmail-remote
 # wget https://raw.githubusercontent.com/qmtoaster/dkim/master/signconf.xml
 # mkdir /var/qmail/control/dkim
 # mv signconf.xml /var/qmail/control/dkim/
 # chown -R qmailr:qmail /var/qmail/control/dkim/
 # openssl genrsa -out /var/qmail/control/dkim/global.key 2048
 # chmod 644 /var/qmail/control/dkim/global.key
 # openssl rsa -in /var/qmail/control/dkim/global.key -pubout -out ./temp.txt
 # cat ./temp.txt | grep -v - | tr -d '\n' | sed '1s/^/dkim1 IN TXT "k=rsa; p=/' &> /var/qmail/control/dkim/public.txt
 # echo "\"" >> /var/qmail/control/dkim/public.txt && rm ./temp.txt
 # qmailctl stop
 # mv /var/qmail/bin/qmail-remote /var/qmail/bin/qmail-remote.orig
 # mv qmail-remote /var/qmail/bin
 # chmod 777 /var/qmail/bin/qmail-remote
 # chown root:qmail /var/qmail/bin/qmail-remote
 # qmailctl start
 # cat /var/qmail/control/dkim/public.txt

  dkim1._domainkey      IN      TXT     "k=rsa; p=******************************"

  Create DNS TXT record for your domain using the output from public.txt above

  Host                                Text
  dkim1._domainkey       	v=DKIM1; k=rsa; p=************************* 

  Your DKIM setup is done.
  To test send mail to any yahoo email id and check headers. If errors show in headers then wait for changes to reflect in DNS.

2. DKIM sign domain with specific key

 # cd /var/qmail/control/dkim
 # openssl genrsa -out ./otherdomain.com.key 2048 && openssl rsa -in ./otherdomain.com.key -pubout -out ./temp.txt
 # chmod 644 ./otherdomain.com.key
 # cat ./temp.txt | grep -v - | tr -d '\n' | sed '1s/^/dkim1 IN TXT "k=rsa; p=/' &> ./otherdomain.com.txt
 # echo "\"" >> ./otherdomain.com.txt && rm ./temp.txt
 # cat /var/qmail/control/dkim/otherdomain.com.txt

  dkim1._domainkey       IN      TXT     "k=rsa; p=******************************"

 Create DNS TXT record for otherdomain.com using the output from the text file 'otherdomain.com.txt'

 Host                                Text
  dkim1._domainkey       	v=DKIM1; k=rsa; p=*************************

 # vi /var/qmail/control/dkim/signconf.xml (Add)

 <otherdomain.com domain="otherdomain.com" keyfile="/var/qmail/control/dkim/otherdomain.com.key" selector="dkim1">
  <types id="dkim" />
  <types id="domainkey" method="nofws" />
 </otherdomain.com>

 So file looks like this:

 <dkimsign>
  <!-- per default sign all mails using dkim -->
  <global algorithm="rsa-sha1" domain="/var/qmail/control/me" keyfile="/var/qmail/control/dkim/global.key" method="simple" selector="dkim1">
  <types id="dkim" />
  </global>
  <otherdomain.com domain="otherdomain.com" keyfile="/var/qmail/control/dkim/otherdomain.com.key" selector="dkim1">
   <types id="dkim" />
   <types id="domainkey" method="nofws" />
  </otherdomain.com>
 </dkimsign>

3. DKIM no signing for domain

 # vi /var/qmail/control/dkim/signconf.xml (Add)

 <nonsigneddomain.com />

 So file looks like this:

 <dkimsign>
  <!-- per default sign all mails using dkim -->
  <global algorithm="rsa-sha1" domain="/var/qmail/control/me" keyfile="/var/qmail/control/dkim/global.key" method="simple" selector="dkim1">
   <types id="dkim" />
  </global>
  <otherdomain.com domain="otherdomain.com" keyfile="/var/qmail/control/dkim/otherdomain.com.key" selector="dkim1">
   <types id="dkim" />
   <types id="domainkey" method="nofws" />
  </otherdomain.com>
  <nonsigneddomain.com />
 </dkimsign>

4. DKIM verification (Spamassassin preferred):

 Assumes:  
   a. 'QMAILQUEUE="/var/qmail/bin/simscan"' defined in /etc/tcprules.d/tcp.smtp 
   b. /var/qmail/bin/qmail-queue is a link.
 Note: Spamassassin has DKIM verification making this unnecessary.
 # qmailctl stop
     Add 'export DKVERIFY=1' to /var/qmail/supervise/smtp/run
     Increase softlimit to 128000000 in /var/qmail/supervise/smtp/run
 # cd /var/qmail/bin
 # wget http://www.qmailtoaster.org/dkimverify.pl
 # wget http://www.qmailtoaster.org/qmail-queue.pl.sh
 # chown root:root dkimverify.pl
 # chown qmailq:qmail qmail-queue.pl.sh
 # chmod 755 dkimverify.pl
 # chmod 4777 qmail-queue.pl.sh
 # unlink qmail-queue
 # ln -s qmail-queue.pl.sh qmail-queue
 # qmailctl start
 Send email to user on the host
 Check email header dkim verification

   Notes: 
          1) In order to test your settings, simply send an email to: check-auth@verifier.port25.com and/or check-auth2@verifier.port25.com
             with the suject of "test" (without the quotes) and "Just testing" in the body (also without quotes). It is best but not required
             to have a subject and body because this service will also show you how spamassassin rated your email. If you have a GMAIL/Yahoo
             email account sending to either or both accounts DKIM signatures could be verified.
             Click to test
          2) To test your DKIM signature wiith OpenDKIM's 'opendkim-testkey' utility install opendkim and run the utility:
             a) # yum install epel-release opendkim*
             b) # opendkim-testkey -vvvv -d otherdomain.com  -k /var/qmail/control/dkim/otherdomain.com.key -s dkim1

                  opendkim-testkey: using default configfile /etc/opendkim.conf
                  opendkim-testkey: /var/qmail/control/dkim/otherdomain.com.key: WARNING: unsafe permissions
                  opendkim-testkey: key loaded from /var/qmail/control/dkim/otherdomain.com.key
                  opendkim-testkey: checking key 'dkim1._domainkey.otherdomain.com'
                  opendkim-testkey: key OK

          3) Testing DKIM signatures sending from Roundcube webmail I found that plain text formatted email caused DKIM failure sending
             to port25.com and GMAIL recipients, but when sending the same email in Roundcube's html format the DKIM signature was verified
             and passed. The same email DKIM signature passed with Squirrelmail, Thunderbird, and OpenDKIM's 'opendkim-testkey' program. It 
             seems that certain email clients will add or subtract characters in the email header causing DKIM to fail. This may be happening 
             in Roundcube while other clients do not affect the email header adversely. I have a help request in the Roundcube user's list
             for this issue. Hopefully, this issue is  merely a configuration setting, if not, that it is resolved soon.