Emailed my friend in Spain two days ago see if they had a good flight and arrived safely by WhatsApp. No reply would they have received message. Thanks for your reply
I agree with Jim that email and Whatsapp are two entirely different things. In my answer above, I assumed that 'emailed' in the question had (incorrectly) been used as a synonym for 'messaged'.
Just a thought...I notice you asked on here 2 days ago how to contact someone in Spain. If you used Whatsapp because of those answers, did you check your friend uses Whatsapp first?
And to add to chelle's answer, if your friend's phone is not connected to the internet by some means then no they wouldn't have been able to read the message nor reply.