Only Allowing Specific Partners email domains to be added and blocking emails with public domain

I have to setup a webapp using Anonymous and forms so please from outside can directly register using FBA pack, add user web part but want to restrict it so people dont use gmail Id or yahoo id rather can only work with specific set of vendors.
You can turn on 'Review Membership Requests' - that would allow you to review every single new registration before allowing them on the site.

If you want to limit who can register at the time of registration (say by limiting the email address domain), you'd have to modify the code to do that. There's nothing in there currently.