Since you only want exact matches on the field, the easiest solution is to make it a string field rather than a text field:
class User < ActiveRecord::Base
searchable do
string :email
end
end
So that you can search for users in your controller like this:
def search
@users = User.search do
with(:email, params[:query])
end.results
respond_to do |format|
format.html { render :action => "index" }
format.xml { render :xml => @users }
end
end
See the Sunspot documentation for more information.