Your hosts file should contain only the following:
fix that and then post the output of the commands you were asked for earlier:
127.0.0.1 localhost.localdomain localhost
18.104.22.168 correo.sanjuan.edu.uy correo
Please enclose the output of each command in 'quotes' to make it easier to read, hightlight a piece of text the hit the quote button (the # symbol) above the text edit box.
dig yourdomain mx
dig yourdomain any
host `hostname` <- note backticks and not single quotes