Email not working

Hi,

I am trying to configure email on outlook, however it seems like something is not working on the server part:
I followed the indications in http://forum.centos-webpanel.com/e-mail/ask-step-by-step-mail-server-setup/:

The hostname error I dont get it, usually the hostname is just the server name, but wont resolve anywhere, right?

Regarding the user to be used: is it the full email or name+domain.com?

And the incoming/outcoming server: is it mail.domain.com or my hostname?

Thank you very much