DKIM Deployment for individual mail domains


For those that have deployed DKIM via the SEA, I have a question regarding enabling DKIM for only a subset of the domains we currently have sending mail.

We have about two dozen domains that are sending email and I want to test DKIM for a single domain/sub.

After adding the private key to the certificates page under the appropriate domain, do I simply enable the outbound policy to add DKIM signatures?

Will this cause issues with the other domains that have not been prepped for DKIM?

Do I need to add an advanced filter to only apply policy to emails containing the header....from []?

Any advise is appreciated.

Documentation seems to be lacking on this topic.