Indispirit wrote: For what it's worth LS email engine is extremely powerful, almost feels like it could become a product on it's own!
The question is what you see as the LS email engine and what method you use to send emails via LimeSurvey.
LimeSurvey as a software will never add DKIM-Support directly. It can't.
You want to reduce issues around SPAM. Use a proper configured SMTP-Server and proper configured DNS, which is allowed to handle your sender Email-address.
If your are not talking about the Software, but the LimeSurvey.org hosting service, it's a bit different. But recommendation still would be to use a SMTP-Server.