No New User Registration Email recieved-- users cannot register to our site

No one can register to my site, because there is no new user confirmation email being sent out. Whenever anyone registers at my site,, they get a page that says, your account is set-up pending your response to the confirmation email. But the email never gets sent out!

I have been looking all over the back end for an email setting... but can't locate a setting. I am using multi-site, pro-sites, with ultimate facebook.