Enhance Security with a New Threading Behavior for Email-To-Case

A new Email-to-Case threading behavior matches incoming emails with their header information instead of through a Ref ID from the subject or body. New outbound emails don’t contain a Ref ID.

Where: This change applies to Lightning Experience in Professional, Enterprise, Essentials, Unlimited, Performance, and Developer Editions.

How: New orgs default to this new threading behavior. Admins for existing orgs can turn the new behavior on or off with a Release Update, until the switch is auto-enforced in Summer '21. Existing orgs continue to work based on ref ID until new behavior is enabled to give time to try out new functionality before auto enforcement.