We are currently using the Jira app Enterprise Mail Handler for Jira to create tickets based on emails in project A. When it creates a ticket, it fills in the summary, description, and custom field "ClientEmail". We have a second project B (called "Personal Directory"), that has tickets with unique data in each ClientEmail field.
We want to use Jira Workflow Toolbox to set up a post-function on project A workflow to link tickets to project B (called "Personal Directory"), based on each unique email address in field ClientEmail. I have been successfully created links based on JQL, but it was for a specific example (see screenshot below). We want Jira Workflow Toolbox to search for data in ClientEmail, and link issue in project A to ticket in project B that already has that same data in its field ClientEmail.
Instead of a specific value, you should use field code for ClientEmail field. You can find its field code in the field list you can field below the configuration parameters of post-function Create issue link. In the following screenshots I show you how to do it. Notice that in my example field ClientEmail has field code %{13600}, but it depends on each specific Jira instance. Configuration of post-function Create issue link:
Once configured, transition configuration will look like this:
I show you a screenshot showing a part of the field list showing the field code for field "ClienEmail":