The following links detail the implementation of EA Domainkeys/DKIM:
Using DomainKeys/DKIM
Deploy Public Key in DNS server
Test DomainKeys/DKIM signature
Troubleshooting
Using Selector
Using Sender Rule
Appendix - Set up SPF record in DNS server
Appendix - Set up DMARC record
Appendix - DKIM/SPF/DMARC Inbound Authentication in Exchange Server
Appendix - Use DkimPowerShell Module in PowerShell