I see the same problem sometimes. I also thought that students are just clicking over and over again on the send button, because I remember some versions ago webwork kept the message on the screen after sending it. But I just checked, and our version 2.15 has a "Return to your work" page after the email is sent.
It is hard to imagine why a student would use the back button and then the send button again.
I also do not get multiple emails when I send them myself from a temporary student account.
It is hard to imagine why a student would use the back button and then the send button again.
I also do not get multiple emails when I send them myself from a temporary student account.