Email Threading for Service Desk System

 For every incoming email, Service Desk software checks 3 email markers to understand whether the email is a reply to an already-existing ticket. If the email is identified as a reply, Service Desk software performs additional sender email checks to make sure it’s not spam.

Email Markers Check

Service Desk software looks for the following three markers in every incoming email. For an email to be threaded to a ticket, it has to pass one of the following checks:

  1. Ticket ID (if enabled)
  2. Message-ID
  3. Unique Identifier

Ticket ID

By default, when a customer creates a ticket in your portal, a ticket ID is generated. The notifications that the customer and agent receive about the ticket updates will carry the ticket ID in the subject line. When the customer or agent replies to these notifications, Service Desk software will check if the ticket ID matches and will thread the reply accordingly.

Service Desk software lets companies that want to send personal replies to their customers remove the ticket ID from the subject line. If the ticket ID is not present, the threading check is done in the following two ways:


Every email has a unique identifier assigned to it by the email provider called Message-ID. (You can read this article to know how you can find the Message-IDs of emails from various email providers).

When you reply to an email, the Message-ID of the original email is available in the ‘In-Reply-To’ or in the ‘References’ section of the email, using which a reply gets threaded to the original email. Service Desk software uses the same method to thread replies to tickets.

Ticket Identifier

Apart from a unique identifier set by the email provider, Service Desk software also has a unique identifier for every email notification sent. This is done using a hidden div tag in the email. As long as the tag remains intact, the email will be threaded properly. For example, if the customer uses the plaintext mode to reply, the ticket identifier will not work.

Email ticket threading will also work when two different businesses use Service Desk software to work with each other. Specifically, each Service Desk software account will add an identifier as part of the email message in the hidden div tag so that ticket threading will work in Reply and Forward scenarios.

Requester Checks

After the ticket is identified as a reply, the requester email should be one of the following for it to be threaded to a ticket:

  • Requester email address of the ticket
  • Agent email address of the ticket
  • Email address(es) in the CC of the ticket
  • Email address(es) to which the ticket was forwarded

So, unless an email satisfies one of the email markers check and one of the sender email checks, it will be created as a new ticket in your helpdesk. If, however, the agent understands that the new ticket is a reply to an existing ticket, they can merge the tickets manually.


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