Workflow on task not firing based on email sent from an object
|Knowledge Article Number||000213837|
Workflow rule not triggered after clicking on send e-mail button from the object, in spite of the completion of the newly created task.
This is an expected behaviour. Please find the explanation below
Similar behaviour is seen for Process builder on Task that has email as a scheduled action.
This behaviour concerns the standard email scenario, where in email is stored in a task. When Enhanced Email is enabled, both a Task and an Email Message are created, it is possible to trigger a Workflow or Process Builder of that record.
Considerations for Setting Up Enhanced Email
Mass mail, does not use Enhanced Email, only a task, and as such, you cannot trigger a workflow / Process on those records.