Email DNS setups for multiple domains using a single domain mail server

[Nathan]

I have multiple domains utilizing one single server for all email. I've 
read multiple documents and got everything setup and working, I think, 
correctly.

My postfix handles all the domains correctly.
My dovecot handles all the users correctly.
My roundcube handles the multiple accounts correctly.

What I'm curious about is my dmarc/dkim setup and my DNS setup.

My primary domain looks like

A   domain.com                  xxx.xxx.xxx.xxx
MX  domain.com                  mail handled by domain.com
TXT mail._domainkey.domain.com  blahblahblahblah
TXT _dmarc.domain.com           blahblahblahblah
SRV _submission._tcp.domain.com directs to domain.com

Each additional domain is setup identically, with their own dmarc and 
dkim, except the mx points back to domain.com
so domain.net would look like

A   domain.net                  xxx.xxx.xxx.xxx
MX  domain.com                  mail handled by domain.com
TXT mail._domainkey.domain.net  diffblahblahblahblah
TXT _dmarc.domain.net           diffblahblahblahblah
SRV _submission._tcp.domain.net directs to domain.net

My question is, do I not need to do any of this for the domains that are 
not actually handling the email, but only for domain.com which actually 
accepts and sends email?

Thanks!