Why do emails thread to the wrong ticket?

Question

An email message threads into an existing ticket as a comment instead of creating a new ticket. Why do emails thread to the wrong ticket?

Answer

When the Zendesk account receives a new email, it reads the message-ID in the email header. If that message-ID matches an existing ticket, the system adds the email as a comment on that ticket. This happens regardless of the support address that receives the email.

Threading logic is based on RFC standards. All In-Reply-To and References lines must contain unique values. If one of these lines uses a static message-ID or email address, incoming emails thread into the same ticket.

Don't remove the text from another email conversation to resend the email and don't change the Reply-To address. To create separate tickets, copy the email content into a new email and send it to the support address.

Note: The system keeps threading header data for 30 days. If an email response to an existing thread is older than 30 days, the data is unavailable to make a connection.

To determine what causes tickets to thread multiple emails into one ticket, examine the original email records for matching message-IDs:

See Open the original message that started the ticket. Open a new window or browser tab to see the original data from the email.

Repeat this for the next threaded message from the same sender that should be a separate ticket.

Select Source for both messages under the subject line to display the header data.

The data in the Source tab covers information that email programs hide. The critical information is listed as one or more of these items:

Message-ID

In-Reply-To

References

If you find Message-ID within the headers, this is the first email written as an original message. Copy the string found next to message-ID and check the References entries for matching messages. Use the Find function (Control-F or Command-F) by pasting the string.

If you find In-Reply-To or References, the message is a reply to an existing message in the requester's email account. Use the Find function to check for more Reference strings for matches. This confirms that the requester replied to saved messages in their inbox instead of submitting a new request. This often happens if the ticket is a follow-up ticket.

Another reason for threading is if the encoded ID from another ticket appears in the email. The system uses encoded IDs to link replies to existing tickets.

For more information, see:

Understanding How Incoming Emails are Matched to Tickets

How are incoming emails threaded to tickets?