mail(2) not working

Hi

I noticed that my clients, when they send me a message over my contact form, are not receiving a copy of their question.

I think, but not sure because I have last tested it a few months ago, this happend since WordPress 5. I did not change something in de mail(2) settings.

Is this a known issue or can you tell me what I can try to make it work again?
I’ve tested it with a gmail and hotmail e-mail adres. I did not receive a copy of what I send over Contact form.

Thanks in advance!

Regards