Desk incorrectly merging similar tickets
We have a process for offboarding employees. Email comes in from HR to our Desk. As it's a partially automated process from their HR template it has similar subject, with similar people CCed for other departments. For some reason Zoho Desk is merging tickets it shouldn't be based on nothing more than subject line. I'll explain:
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Email comes in yesterday with subject "No Longer Employed - John Smith". Creates ticket number 788. So we process ticket and do what we need to do. Send email and close ticket 788.
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Today email comes in "No Longer employed - Jane Doe". But Zoho automatically appends the second email to the first ticket. So in Zoho Desk, there is no ticket created for Jane Doe, only a reply to 788 with the info for Jane Doe as a reply to the John Smith ticket. Ticket is reopened due to client response, which doesn't send out the proper 'new ticket created' email to the IT department. Any reply to the ticket note for Jane Doe go out with the "[#788#] No Longer Employed - John Smith" subject.
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I've already confirmed that the second email is a 'fresh' email, and not a reply to previous ticket. How can I stop this annoyance? This has happened server times. I have even see it append 4 separate emails into 1 ticket for no reason.