Same problem as haiflosse2, but on two different sites using different hosting and different themes (both hosting companies are reputable.)
Updating to 3.0 broke only the order notifications for me. Customer notifications still worked.
Updating to 3.0.1 this morning has broken all email notifications (customer, admin) on both sites. The system shows the orders but no emails are being received. I’m using different customer emails for the tests, just to be sure it’s not an email problem. And the WC shops on two different sites.
Non-WC email functionality (i.e. reviews, comment spam!) worked normally both post 3.0 and now with 3.0.1.
Hope this helps someone because the WC helpdesk have gone very quiet…