I am not running DNS at all on ispconfig. Nor are we running email. (postfix is installed as a standalone internet site from the installer.) eg: the box is just serving websites, nothing else. I can see an SMTPD key in /etc/postfix, but I can't find the dkim text file needed anywhere to add to our DNS server. Under the server->config->mail tab the dkim path shows as : /var/lib/amavis/dkim Which does not exist. how do I generate the dkim file needed in this scenaio?
.... and I should also add we have domain wide dkim set already in our dns for our other systems... so should I be importing rather than generating?
If you don't run email services, then you can't sign emails with DKIM on that server. DKIM signing is part of the ISPConfig mail services setup and done by Rspamd or Amavisd which you seem to have not installed.
If you want your website to send email that gets DKIM signed, configure it to authenticate to and send through your mail server. You could also do that at the MTA level on your web server, eg. for postfix refer to the SASL howto (and search the web for how to configure other MTA's), but I would personally just configure each website to send correctly.
