[Solved] Add DKIM to outbound emails for domain but disable receiving?

I've tried to find an answer to this before asking, and so if there is one, please point me to it and shame me!

Summary
I've been going through domains at my organization and making sure SPF, DKIM, and DMARC are all set up correctly. Our organization manages email through 365, so setting everything up was a cake walk.

I wanted to make sure messages from our website look legit too, so I set out to enable DKIM there via ISPConfig. To achieve this, I added the domain under "Email", generated the keys and added the records to my DNS.

It's working great for the most part and I am grateful for ISPConfig.

Problem
Email sent from the server now looks locally for users of that domain and removes them when "user unknown" is returned. It delivers a nice, DKIM signed message to everyone else.

What I've Read
In other threads about this, people asked why enable email for a domain if that server isn't handling it? Their recommended solution is to remove the domain and let things go back to normal. That doesn't address the issue of signing website generated emails though.

I've also looked into Email Routing but from what I could find, that wouldn't get around the local lookup for recipients.

What I am Asking (am I missing something simple?)
Is there a way to keep DKIM signing on outbound emails, but disable local user lookup when sending for that domain?

I appreciate any insight.

 

Thanks Th0m, I'll do that!