How can we add new DKIM entries when the domains are added using postfixadmin?

Is the following correct procedure? What will happen if I do not add DKIM entries?

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1. Generate the new key.

cd /var/lib/dkim/
amavisd genrsa xyz.com.pem
chmod 0644 xyz.com.pem

2. Add it to your amavisd.conf file:
Search for "# Add dkim_key here.", and add it alongside the others, preferably in alphabetic order so you can find it faster.

dkim_key("xyz.com", "dkim", "/var/lib/dkim/xyz.com.pem");

3. Add your new domain to @local_domains_maps in amavisd.conf. The line should now read something like this:

@local_domains_maps = ( [".$mydomain", "firstdomain.com", "xyz.com"] );  # list of all local domains

4. Restart amavisd

/etc/init.d/amavisd restart