Answer:
Yes, the sample is a voluntary response sample.
Explanation:
A voluntary sample is a sample response produced by volunteers. Its a type of non-probability sampling methods where people self-select themselves whether to take part in any survey or not. Like online polls.
So, yes this scenario is a voluntary response sample. The students who got the mail can reply or not reply. It fully depends on them whether they want to take part in the survey or not. If they took part, it will be completely voluntarily, as no one is forcing them to do so.