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By default configurations in JEMH when the email has been sent and the issue is created in Jira, the notification received of the issue creation notification will create a new email Thread thread and all further communication will be associated with this newly created email Thread. In order to associate the issue creation notification and all other event notifications with the initial email sent requires to apply additional configurations. The following example is based on using a Gmail email client.
Gmail requirements to satisfy the email threading
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The initial email has been sent to create an issue in the Jira
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The issue has been created and the custom field has been populated with the Email value
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