Messages thread into an existing ticket as a comment instead of generating a new ticket. Why do emails thread to the wrong ticket?
When a new email is received, Zendesk scans the message-ID on the email. If that message-ID matches an existing ticket then the email is added as a comment on the existing ticket. Zendesk does this regardless of the support address the email is received at.
Threading logic is based on RFC standards. All
References lines should contain unique values. If one of these lines uses a static message-ID or email address, Zendesk will thread incoming emails into the same ticket.
Ensure that you are not removing all of the text from another email conversation and resending it or just changing the
Reply-To address. To create separate tickets, copy the email content into a new email and manually send it to your support address.
For more information, see the article: Getting started with email - Part 1: How the email channel works.