DKIM is an acronym for DomainKeys Identified Mail. It is an email authentication method to ensure the content of a message has not been altered in transit.
At this time, Paubox does not support DKIM signing for individual customers. We validate all emails by adding our SPF record to our customer's domain records and have found that this has been sufficient for ensuring the deliverability of all emails. For more information about SPF records, please see this article.