Adds a reaction of the caller to the email and publishes an EAppMailReactedEvent. A user may have several reactions on an email, but only one per reaction value. Returns the updated record.

The record is looked up within the caller's tenant, and the caller must also be allowed to access the entity the email is linked to (employer, customer, lead, workflow or meeting, checked in that order); otherwise that entity's access check rejects the request. The caller also needs the update permission of the linked entity type (employers:write, leads:update, workflows:update, customers:update or meetings:update), checked in the service layer.

Errors: 400 if the caller already has this reaction; 403 if the update permission is missing; 404 if the record does not exist in the caller's tenant.