Sending and receiving emails on my iMac

Please refer to If you can’t send or receive email on your Mac

The suggestions in the link provided above should be checked out. You say that you "have done what they have asked and nothing works." That is not useful information. It would be helpful to know specifically what it is that you have done and what the results were. Then we have a better idea of what might be happening. Also, you can contact your email service provider for their assistance. They can quickly determine what is or is not happening at their end.