Email To Case Thread Id linking issue

Question

I observed our sandbox does not have Thread id feature as we have created this org after recent release of salesforce where Message-ID and reference header is activated. What I want is that customer once send an email, a case is created. Now they got an custom vf email back saying your case has been created. But next feature we want to provide to customer is that if they send another email, we want to link that email as well to the case just created (we can ask them to add the unique string in the email they got so that salesforce understand that this email is also linked to existing email). Remember customer here is NOT replying back to the original email. Since I am new to this feature getting activated, can someone please help me out how I we can achieve this.

Answer 1

As per the latest updates, disabled Ref Id and New Threading Behavior for Email-To-Case.

With the new behavior, incoming emails are matched to cases using the Message-ID in their In-Reply-To and References headers rather than through a Ref-ID from the email subject or body. Once email header-based threading is enabled, Email-to-Case no longer inserts a Ref-ID in outgoing emails and ignores the Ref-ID from incoming emails for matching.

You can replace your apex method related to the VF page from getCaseIdFromEmailThreadId to getCaseIdFromEmailHeaders

The new method can retrieve the Case ID from replies to emails sent by agents from the case email composer.

for more details, refer the help article Link