Servers must use approved DoD certificates.
Server certificates are required for many security features in Exchange; without them the server cannot engage in many forms of secure communication. Failure to implement valid certificates makes it virtually impossible to secure Exchange's communications.
Remove the non-DoD certificate and import the correct DoD certificates.
Open the Exchange Management Shell and enter the following command: Get-ExchangeCertificate | Select CertificateDomains, issuer If the value of 'CertificateDomains' does not indicate it is issued by the DoD, this is a finding.