Mac will not send or receive email

It would be helpful if you would provide us with some specific details of what is going on. Have you changed anything? Have you confirmed that you do have internet access using a browser? Are you able to access the internet provider's web site with a browser and get mail?

Until and unless you are able to provide some useful details there is little we can do for you. It would amount to our only guessing as to what the issue is.