Request Queue Submission by Email - Turn off bounce for non-users

I want to be able to auto-submit to a request queue when someone sends an email to an email alias if they have a Workfront account. But not all requesters through the alias have WF accounts & the auto generated email reply would cause questions. I'd still want the failure notification to forward to me if it failed, but not the requester. This would save us from forwarding (or manually submitting) every request that comes through vs only ones that failed.

The email SL bounce back is: Your issue was not added to Creative Requests.

I would just like this turned off, or if easier, I would be happy with custom email reply.