Why l cannot receive incoming emails even if have set all the informations correctly?

I have bought and registered a new email account, and l have set up all the informations on Mail (also with the technical support of my email provider) and there is no way to receive the emails.

I can send them in Outbound, but the Inbound id not working.

YES all the informations provided in Mail are correct!

My email provider said to contact Mac and ask for clarifications, because there is anything we can do from our end.

Can anybody explain why? All other accounts are working fine.

Thank you.