Salesforce Auto-Response Emails Sent from Unexpected User When No Rule Entry Matches

If Cases are sending an auto-response from a User that isn't defined as the Sent From (Email) in any of your rule entries, the auto-response may be coming from the "Default Response Template" setting.

Classic Steps to Check Default Response Template

Classic Steps:

Under Setup | Customize | Self-Service | Web-to-Case | Modify | Default Response Template

OR

Under Setup | Customize | Leads | Web-to-Lead | Default Response Template
 

Lightning Steps to Check Default Response Template

Lightning Steps:

Setup | Feature Settings | Marketing | Web-to-Lead   OR   Setup | Feature Settings | Service | Web-to-Case

Which says: "Use Case/Lead Auto-Response Rules to select different email response templates based on attributes of the cases/leads submitted online. Cases/Leads not matching any of the rules will be sent the default response template selected below."

This template will be sent from the User triggering the auto-response rule.

If a Case is created online, goes through auto-response rule entries, and doesn't meet criteria on any entry, then the Default Response Template is sent from the current User.

This behavior occurs because the Default Response Template is sent from the currently logged-in user when no auto-response rule entry criteria are met. Identifying and removing or replacing this default template resolves the issue.