No, you cannot add emails with the same subject line to an existing ticket as a comment. Emails must have matching message-IDs to be threaded into existing tickets. This is a hard-coded feature in Zendesk and cannot be changed.
If you're looking to manage your email threads more effectively, it's important to ensure that the message-ID of the email matches the existing ticket. This is the only way to ensure that emails are added as comments to the correct ticket. For more details, you can refer to the article: Why do emails thread to the wrong ticket?
Emails cannot be configured to thread into existing tickets unless they have matching message-IDs. This is a hard-coded feature in Zendesk. The system relies on message-IDs to determine whether an email should be added as a comment to an existing…
For an email to be added as a comment to an existing Zendesk ticket, it must have a matching message-ID. This is a non-negotiable requirement. The message-ID is used by Zendesk to identify whether an email should be threaded into an existing…