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JUNCTIONIDLIST
Returns a JunctionIDList based on the provided IDs.
A JunctionIDList is a string array of referenced ID values that represent the many-to-many relationship of an underlying junction entity.
Use
JUNCTIONIDLIST(id,
id,...) and replace id with the Salesforce ID
you want to use.
JUNCTIONIDLIST(Case.ContactId)
This formula returns the case’s contact record ID. When used on the email action for cases, you can use this formula as a predefined value for the To Recipients field. Using this formula as a predefined value for the field ensures that sent emails are always associated with a Salesforce record. In the case feed publisher, users see the contact name instead of the ID or email address.

