No Email after assign task to user

ERPNext
1

I have many Tasks, once I assign a task to the user it should send an email, but he didn’t send an email?
What is the problem?

Note : email setting is good, and I test send something from ERPNext to email, and I receive an email .

2

It seems this should be a core feature. I too was surprised to see there was
no email generated after assigning a task. There is no indication via desk either.