When Cases are created via Email-to-Case with Deliverability set to "All Emails," the Auto Response email may not be sent even when email logs show no outbound activity and debug logs confirm the Auto Response Rule was matched.
This occurs because sending an email from a Case automatically creates a Task, and if a Validation Rule or Trigger on the Task object fails, the email is silently not sent without displaying an error to the end user.
To troubleshoot further, administrators can manually test the process using the Send an Email button from the Emails related list on the Case.
Use the same email template configured in the Auto Response Rule and send it to the same recipient email address. This simulates the Auto Response process through the Salesforce UI.
If a validation error appears during this test, it indicates that Validation Rules or Trigger logic on the Task object are preventing the Task from being created successfully.
When an email is sent from a Case — including through the Send an Email action, Email Publisher, or an Auto Response Rule — Salesforce automatically creates a Task record associated with that email activity.
During Task creation:
If the Task fails validation or Trigger processing, Salesforce prevents the Task from being created.
Because the email activity depends on successful Task creation, the email itself is also not sent.
In UI-based actions such as Send an Email, users may see a visible validation error.
However, for Auto Response Rules triggered through Email-to-Case, the process occurs in the background and no visible error message is displayed to the end user.
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