In a previous blogpost, I already discussed DKIM signing with Exchange 2016: SenderID, SPF, DKIM and DMARC in Exchange 2016 – Part II
Exchange out-of-the-box does support SPF checking, but DKIM signing/verifying and DMARC verifying are not supported. There are free 3rd party tools for DKIM Signing that can be found on GitHub, but at the moment of writing this tool only supports DKIM Signing, but does not support DKIM verifying. I have to admit that DKIM signing with this tool works very well.
I already explained earlier that I’ve installed and configured a Cisco Email Security Appliance (ESA, previously known as IronPort) appliance in my lab environment, and this is installed like this:
Figure 1. My testlab Exchange environment.
All outbound SMTP mail is via the ESA. The FQDN of the ESA is smtphost.exchangelabs.nl, of course it has a public IP address with a corresponding PTR record.