check mx records for disposable emails

app/create.rb

@@ -84,6 +84,11 @@ post '/create' do
     return {result: 'error'}.to_json
   end
 
+  if Site.disposable_mx_record?(@site.email)
+    flash[:error] = 'Cannot use a disposable email address.'
+    return {result: 'error'}.to_json
+  end
+
   @site.email_confirmed = true if self.class.development?
   @site.save
 

models/site.rb

@@ -546,16 +546,33 @@ class Site < Sequel::Model
     !username.empty? && username.match(/^[a-zA-Z0-9_\-]+$/i)
   end
 
+  def self.disposable_email_domains
+    File.readlines(DISPOSABLE_EMAIL_BLACKLIST_PATH).collect {|d| d.strip}
+  end
+
+  def self.disposable_mx_record?(email)
+    email_domain = email.match(/@(.+)/).captures.first
+
+    begin
+      email_mx = Resolv::DNS.new.getresource(email_domain, Resolv::DNS::Resource::IN::MX).exchange.to_s
+      email_root_domain = email_mx.match(/\.(.+)$/).captures.first
+    rescue => e
+      # Guess this is your lucky day.
+      return false
+    end
+
+    return true if disposable_email_domains.include? email_root_domain
+    false
+  end
+
   def self.disposable_email?(email)
     return false unless File.exist?(DISPOSABLE_EMAIL_BLACKLIST_PATH)
     return false if email.blank?
 
     email.strip!
 
-    disposable_email_domains = File.readlines DISPOSABLE_EMAIL_BLACKLIST_PATH
-
     disposable_email_domains.each do |disposable_email_domain|
-      return true if email.match /@#{disposable_email_domain.strip}$/i
+      return true if email.match /@#{disposable_email_domain}$/i
     end
 
     false