The field usually is blank because the php.ini file normally has the mail server settings.
You would need to contact your host to find out the smtp server name.
But also you should try testing the email account listed in the board email address as Gizmo stated,Outside of UBB.
All email sent from the board comes from what is entered in that setting.
It could be there is a typo in the address or the email account just does not work.
Or it could be the email address is blacklisted.( happened to me twice)
