Making sense of the Case Thread Id
For those using salesforce for service & support and email to case you may already be familiar with the thread Id. The thread Id is included in the subject and body of email’s sent from salesforce (relating to an existing case) which acts as a unique identifier in order to automatically relate replies to the correct thread in salesforce. This is helpful if you want to avoid creating new, duplicate cases from an auto-response reply.
The thread id is actually a combination of your salesforce org Id and the case record Id. If you’d like to create the thread id for custom objects or any other reason, you can use the following formula:
"ref:00D"&MID(Id,4,1)&RIGHT($Organization.Id, 4) &"."& LEFT(Id,4)&RIGHT(Id,5) &":ref"