Have you checked the message queue to see if the message shows up there and if it shows as sent?
There’s a big difference between the email not sending and the email sending but not being received, it changes where the problem may be.
So, in Event Espresso does it show the message as sent or failed?
The message queue has a ‘status bar’ to the left of each message if you go to Event Espresso -> Messages -> Message Activity you’ll see a list of all messages in the queue, can you see the email there? What color status bar does it have?