This is the same exact issue as https://jira.atlassian.com/browse/JSD-4058, which was initially reported with only Cloud cases and was thus resolved in Cloud, but not yet in Server.
When public signup is enabled in a Service Desk, and a customerA sends in an email while CC'ing customerB, an issue is correctly created.
When customerB replies to customerA's original email, customerB's new issue is created, rather than the reply being a comment on customerA's ticket.
JIRA Service Desk 3.2.1
- Create new service desk project and set it as open for public sign up
- Setup email channel for the project
- As customer A, send email to the sd email channel and cc customer B (A new issue will be created in Service Desk project)
- As customer B, after receive the email from customer A, reply the email (Note this is the original email from A, not Service Desk generated email) with comment
Reply from B will be added as comment to the issue
A new issue has been created.