Auto-email to technician

I dunno what went wrong.

I ticked at "Notify technician(s) by email when a new request is created"

When I received an e-mail request, I assign the request to a particular technician, but there was no e-mail received by him.

I click on Task->Notify->E-mail the Technician button, it works fine. (Manually)

Is it something wrong with my SD setup?

Thank you