Disable Ref ID and Switch to Lightning Threading

When will Salesforce enforce the Disable Ref ID and Transition to New Email Threading Behavior release update?

[Winter '25 Update] Salesforce no longer plans to enforce the Disable Ref ID and Transition to New Email Threading Behavior release update. We previously announced the update would be enforced in Spring '25. We strongly recommend you enable the update and migrate to Lightning Threading, as it's more secure at threading emails to cases than RefID.

What is the change?
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. Starting Spring ‘23, Email-to-Case supports a new email threading approach called Lightning threading. 

In this new threading behavior, incoming emails aren’t matched using Ref ID strings. Instead, they’re matched using a secure token in the email subject or body. When no match is found using token-based threading, Email-to-Case uses header-based threading and checks metadata in email headers. 

The “Disable Ref ID and Transition to New Email Threading Behavior” release update allows orgs to transition to Lightning threading. It replaces a release update that was first made available in Winter ’21 to transition from Ref ID threading to header-based threading.  

Why is Salesforce delivering this change?
Lightning threading is a secure method of email threading that helps to match incoming and outgoing emails to related cases. Because Lightning threading combines token- and header-based threading, Email-to-Case finds corresponding cases more reliably and avoids creating a new case when a related case exists.

Why the name Lightning threading?
This new threading approach is supported in Lightning Experience. Salesforce recommends that customers migrate to Lightning Experience to take advantage of the latest innovations and product features. 

How Is Lightning Threading Different from Ref ID Threading?
In Lightning Threading, Email-to-Case inserts a token into the email body or subject of an outgoing case email. A token is a uniquely formatted string generated to meet Salesforce security standards. When a customer replies to the outgoing email, Email-to-Case looks for the token to match the reply to the related case. If no token match is found, Email-to-Case falls back to header-based threading. If neither method identifies a matching case, Email-to-Case creates a new case.
After transitioning to Lightning Threading, Email-to-Case no longer inserts a Ref ID in outgoing emails and ignores Ref IDs in incoming emails for matching.


When was the release update first available to customers?
The release update to transition to header-based threading was first available in Winter ’21. We modified that update to transition to Lightning threading in Spring ’23.

What changes did Salesforce introduce related to this release update?
We’ve received a tremendous amount of feedback on Lightning Threading from our early adopters. Thank you! We have been committed to improving our functionality to meet the standards of our customers.

• Summer ’20: Starting in this release, Salesforce automatically saves the Message-ID of all standard emails sent and received by Email-to-Case.
• Winter ’21: Starting in this release, all new orgs default to the email header-based threading mechanism and Ref ID-based threading is no longer recommended.
• Summer ’21: Starting in this release, email header-based threading is supported for case email alerts sent by Flows or Process Builder processes.
• Winter ’23: Starting in this release, email alerts contain information to identify the related case in the Message-ID, regardless of whether or not header-based threading is enabled.
• Spring ’23: Starting in this release, all new orgs default to Lightning threading. Lightning threading is now the recommended threading approach and includes a merge field and Apex methods, similar to Ref ID.
• Winter ’24: Salesforce announces that Lightning threading will be enforced in the Spring '25 release. 
• Spring ‘24: Salesforce enables a new header-based threading preference, giving customers the flexibility to choose how emails are threaded.

• Spring ’25: The Disable Ref ID and Transition to New Email Threading Behavior release update is scheduled to be enforced.

How has Salesforce communicated the threading and release update changes?
To advise customers about the change to Lightning threading, we recorded a webinar on December 16, 2022. Previously we communicated the transition from Ref ID to header-based threading with published release notes about the release update, a CSG webinar, and a technology communication email.  

How can I tell which threading approach is in use currently?
Go to the Email-to-Case page in Setup.

• If you see settings named Insert thread ID in the email subject and Insert thread ID in the email body, you’re using Ref ID threading. Enable the release update to switch to Lightning threading.
• If you don’t see those settings, you’re using Lightning threading or it’s available in your org. To get the full case-matching benefits of Lightning threading, we recommend:
  • Select Insert email threading token in email subject, Insert email threading token in email body, or both: This turns on the token-based component of Lightning threading. Verify that the settings you see contain the word “token”.
  • Select Use email headers for threading: This turns on the header-based component of Lightning threading.