You can use the following cPanel script to install domainkey for an account
Where username is the cPanel user.
If you get an error similar to “Domain keys are not installed on this machine.” you either are not running the latest release or current version of cPanel or you have not converted yet to maildir. Maildir conversion is required before you install DomainKeys.
Ok, we just installed DomainKeys for a domain, but how about if we want to install it for all the domains (users)?
Well, you can use the following script for it.
for i in `ls /var/cpanel/users` ;do /usr/local/cpanel/bin/domain_keys_installer $i ;done
You can contact our customer suport team if you are facing any issues.