Email threading is the process of matching incoming and outgoing emails to a related case so that a collection of related emails appears in the case feed.
Email threading ensures that outgoing emails and incoming responses related to a customer inquiry are associated with the same case in Salesforce. Threaded emails appear in the case feed so service reps and supervisors can quickly grasp an inquiry’s history and status.
Email-to-Case previously used a threading method called Ref ID threading, and later added support for an alternative method called email header-based threading. Email-to-Case is now transitioning to Lightning threading, a more secure method that combines header-based and token-based threading.
email threading token is a secure, uniquely formatted string that is embedded in outgoing emails to help automatically link incoming replies back to the correct record, like a Case, in Email-to-Case. It functions similarly to a Ref ID but is designed to meet Salesforce's security standards. When a customer replies to an email containing this token, Email-to-Case uses it to identify the relevant record and attach the reply, keeping the conversation organized.
This process reminds me WhatsApp business and the way my customers gets automated response from me in my absence.
"Email-to-Case Threading Salesforce. Help Salesforce [Online]. Available at: URL [17/06/2025]"