DE server mail address is set to de_instance@<WorkloadAutomation>.<com>. How does a user change this address?
Workload Automation DE: Any version
By default, DE server mail address is set to de_instance@<WorkloadAutomation>.<com>. This domain may be blocked by SMTP / Mail server as customer organization will be different.
In Desktop Client, navigate to Admin -> Topology. Right-click on the server and then on Configure Shared Parameters. In the tab on the right, expand Email section and change "Email address to identify CA WA Server" to a valid email address.