==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 0.9.8
- Linux/BSD distribution name and version: centos 7
- Store mail accounts in which backend (LDAP/MySQL/PGSQL):  MySQL
- Web server (Apache or Nginx): Nginx
- Manage mail accounts with iRedAdmin-Pro? no
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====

Under @dkim_signature_options_bysender_maps = ({

THis was noted
[b}# catch-all (one dkim key for all domains{/b}
    '.' => {d => 'mydomain.com',
            a => 'rsa-sha256',
            c => 'relaxed/simple',
            ttl => 30*24*3600 },

I took this to mean that this was a catch-all and I did not need to add additional domains here for this server. It seemed to be correct. I duplicaed mydomain's dkim entry into new_domain DNS and tested the dkim over at mail-tester.com. And it passed. 

Does this sound right??