My organization has 2 mail servers. One is our MS Exchange server for corporate mail. The other is an SMTP server (not Exchange) our application uses to send automated email notifications to our users. Both servers send from
@example.com, though each server has a separate public IP.
I'm wondering if there is a downside to implementing DKIM only for our automated email server (as it seems Exchange doesn't support DKIM out of the box). It's not clear if a partial implementation would hurt mail sent without DKIM.