How to get the email id of new created email from a workflow step in custom workflow?

I am working on a workflow where I need to get the email id of a new created email in the previous step of Workflow, which I am planning to use to pass as Input Parameter to a custom Workflow.

Here is what I am trying to do.

In custom workflow I am trying to retrieve that Email Id.

[Input("SourceEmail")]
 public InArgument<String> SourceEmail { get; set; }
String sourceEmail = SourceEmail.Get<String>(executionContext);

But instead I am getting empty string. Any idea how can I get this ?