Question
Messages thread into an existing ticket as a comment instead of generating a new ticket. Why do emails thread to the wrong ticket?
Answer
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 In-Reply-To
and 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.
19 Comments
We have an instance where we have an external support provider that sends us ticket notifications [via ConnectWise, I believe] which always come with the subject:
Ticket#XXXXX/Location/Issue
Each time their ticketing system generates a response [whether to us or another third party or to their own office] it creates a new ticket.
How can I have a trigger based on subject to check if the Ticket#XXXXX exists and thread into that if so?
Hi Americo,
That's a good question. Right now, business rules in Zendesk (triggers and automations) do not have the function to thread emails to existing tickets. Also, while triggers are able to check the subjects of tickets, it would only be for checking it for a specific word or thread. There is no way for a trigger to check the subject and cross-reference it with all the existing tickets.
I would suggest posting this as a feature request though, as I do see how this can be useful. Feel free to post this here: https://support.zendesk.com/hc/en-us/community/topics/200132066--Feedback-on-Support
Cheers!
Marco M. | Zendesk Support
How can we check the message ID, when the issue is replies from email to a chat conversation, where we cannot check any message ID on the original message because it originated from Zendesk?
To check the message ID of an email, you can open a ticket created by inbound email and you have the option to view and download the original email.
Please see Viewing the HTML and original source for incoming tickets for more information.
Trust this helps.
Hi Rad,
Those instructions do not work for the situation I have laid out, thus my question.
Hello CJ Johnson!
Thanks for the follow-up! We're sorry to hear the initial instructions were not ideal for your use case.
I'd like to refer you to this other article regarding Customers not receiving emails. The events should show a Trigger notification with a number that Advocates can use to track down logs internally. Although we wouldn't be able to check logs every time, if you're having specific issues, feel free to contact us via WebWidget Messaging and we'll be happy to help further.
In short, "Message-IDs" are only available for inbound email messages, not outbound, but if you replied to an actual email, the Message-ID should remain the same for the entire thread, and that's how Zendesk links all messages in the same ticket. Hope that makes sense! :)

Ex.
Hi Anna Lainfiesta
We have external system sends emails to Zendesk and every time in generates new ticket in Zendesk despite the Subject, Sender and Receivers are the same?
Can you recommend the way to configure in a way that Original ticket gets updated instead of generating new ones every time.
Thanks.
As explained in this article, if
In-Reply-To
andReferences
lines are different it will be threaded on a different ticket or create a new one. It's possible that your external system is changing these values. Due to this, the only recommendation we can provide it to work with the system admin to make sure that no changes will be made to the emails they will send to Zendesk.Hi Zendesk Team,
I have one ticket (#abcd) in particular where Requesters had history of sending new ticket to support+idabcd@mycompany.com, which we have already advised requester to send to support@mycompany.com instead.
Requesters Forwarded the email (where he sent to support+idabcd@mycompany.com) to the correct support@mycompany.com without the wrong address, but the new email still threaded to #ticketabcd.
Please advise if this should be the correct behavior?
It looks like you have a ticket open with our Customer Care team regarding this issue. They will follow up with you as soon as they can to troubleshoot further so stay tuned.
Cheers!
Is there any way to have an email reply processed by Zendesk as a comment on an existing ticket, without the original message-id in the In-Reply-To header?
We tried adding the ticket email address to the "References" header, but that just resulted in the message being flagged with the error "Permission denied due to unauthenticated email update".
The message-id is required for the email operation on an existing ticket. As you can see addressed in the article: 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.
I hope this answers your question! Thanks!
It also mentions using the References header. If the References header has a value such as support+id1234@domain.tld, does Zendesk honour that as a link to the original ticket of 1234 for comment? Or does it only use the original message-id and only in the In-Reply-To header?
Quoting from the article above, "If one of these lines uses a static message-ID or email address", where "these" refers to the In-Reply-To and References headers.
If you'll use the support+id1234@domain.tld it will still be threaded on the same ticket. However, it will have a banner pertaining to the user as not part of the conversation. There's also a possibility that the reply coming from that email address will be suspended like what happened on my test. It will only be visible on the ticket once you have recovered it.
The one in the red box was a user not part of the ticket that used support+id1234@domain.tld. Meanwhile, the requester (green box) also used support+id1234@domain.tld and it was threaded on the same ticket.
This is not accurate. I have messages with unique message-IDs threading together.
CJ - would you mind sharing some notes on the SMTP headers used to accomplish this?
Longboard I literally just downloaded the original email source from multiple emails in a thread that I knew should never had threaded, and lo and behold, the message ID in each is very different, yet they are threading into a single ticket. They also all have unique subject lines.


I believe the original answer is confusing/wrong - each email will have a unique 'Message-ID' the key to any reply emails being linked to an existing ticket is that the new email will have an 'In-Reply-To' id that is the same as the 'Message-ID' of an email in an existing ticket.
So this
"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."
would be more accurate if it said
"When a new email is received, Zendesk scans for any 'In-Reply-To' id on the email. If the 'In-Reply-To' id matches an existing tickets Message-ID then the email is added as a comment on the existing ticket."
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