added email whitelist SiteSetting feature to replicate email blacklist. email_validator method now also uses the regex method for both the whitelist and blacklist.

app/models/site_setting.rb

@@ -33,6 +33,7 @@ class SiteSetting < ActiveRecord::Base
   client_setting(:flush_timings_secs, 5)
   client_setting(:supress_reply_directly_below, true)
   client_setting(:email_domains_blacklist, 'mailinator.com')
+  client_setting(:email_domains_whitelist)
   client_setting(:version_checks, true)
   client_setting(:min_title_similar_length, 10)
   client_setting(:min_body_similar_length, 15)

app/models/user.rb

@@ -532,14 +532,22 @@ class User < ActiveRecord::Base
     end
 
     def email_validator
-      if (setting = SiteSetting.email_domains_blacklist).present?
-        domains = setting.gsub('.', '\.')
-        regexp = Regexp.new("@(#{domains})", true)
-        if self.email =~ regexp
+      if (setting = SiteSetting.email_domains_whitelist).present?
+        unless email_in_restriction_setting?(setting)
+          errors.add(:email, I18n.t(:'user.email.not_allowed'))
+        end
+      elsif (setting = SiteSetting.email_domains_blacklist).present?
+        if email_in_restriction_setting?(setting)
           errors.add(:email, I18n.t(:'user.email.not_allowed'))
         end
       end
     end
+    
+    def email_in_restriction_setting?(setting)
+      domains = setting.gsub('.', '\.')
+      regexp = Regexp.new("@(#{domains})", true)
+      self.email =~ regexp
+    end
 
     def password_validator
       if (@raw_password && @raw_password.length < 6) || (@password_required && !@raw_password)

config/locales/server.en.yml

@@ -356,6 +356,7 @@ en:
     supress_reply_directly_below: "Don't show reply count on a post when there is a single reply directly below"
     allow_index_in_robots_txt: "Site should be indexed by search engines (update robots.txt)"
     email_domains_blacklist: "A pipe-delimited list of email domains that are not allowed. Example: mailinator.com|trashmail.net"
+    email_domains_whitelist: "A pipe-delimited list of email domains that users may register with. WARNING: Users with email domains other than those listed will not be allowed."
     version_checks: "Ping the Discourse Hub for version updates and show version messages on the /admin dashboard"
 
     port: "Use this HTTP port rather than the default of port 80. Leave blank for none, mainly useful for development"

spec/models/user_spec.rb

@@ -471,7 +471,12 @@ describe User do
       Fabricate.build(:user, email: 'notgood@trashmail.net').should_not be_valid
       Fabricate.build(:user, email: 'mailinator.com@gmail.com').should be_valid
     end
-
+    
+    it 'should not reject partial matches' do
+      SiteSetting.stubs(:email_domains_blacklist).returns('mail.com')
+      Fabricate.build(:user, email: 'mailinator@gmail.com').should be_valid
+    end
+    
     it 'should reject some emails based on the email_domains_blacklist site setting ignoring case' do
       SiteSetting.stubs(:email_domains_blacklist).returns('trashmail.net')
       Fabricate.build(:user, email: 'notgood@TRASHMAIL.NET').should_not be_valid
@@ -494,6 +499,38 @@ describe User do
       u.email = 'nope@mailinator.com'
       u.should_not be_valid
     end
+    
+    it 'whitelist should reject some emails based on the email_domains_whitelist site setting' do
+      SiteSetting.stubs(:email_domains_whitelist).returns('vaynermedia.com')
+      Fabricate.build(:user, email: 'notgood@mailinator.com').should_not be_valid
+      Fabricate.build(:user, email: 'sbauch@vaynermedia.com').should be_valid
+    end
+
+    it 'should reject some emails based on the email_domains_whitelist site setting when whitelisting multiple domains' do
+      SiteSetting.stubs(:email_domains_whitelist).returns('vaynermedia.com|gmail.com')
+      Fabricate.build(:user, email: 'notgood@mailinator.com').should_not be_valid
+      Fabricate.build(:user, email: 'notgood@trashmail.net').should_not be_valid
+      Fabricate.build(:user, email: 'mailinator.com@gmail.com').should be_valid
+      Fabricate.build(:user, email: 'mailinator.com@vaynermedia.com').should be_valid
+    end
+
+    it 'should accept some emails based on the email_domains_whitelist site setting ignoring case' do
+      SiteSetting.stubs(:email_domains_whitelist).returns('vaynermedia.com')
+      Fabricate.build(:user, email: 'good@VAYNERMEDIA.COM').should be_valid
+    end
+
+    it 'email whitelist should not be used to validate existing records' do
+      u = Fabricate(:user, email: 'in_before_whitelisted@fakemail.com')
+      SiteSetting.stubs(:email_domains_blacklist).returns('vaynermedia.com')
+      u.should be_valid
+    end
+
+    it 'email whitelist should be used when email is being changed' do      
+      SiteSetting.stubs(:email_domains_whitelist).returns('vaynermedia.com')
+      u = Fabricate(:user, email: 'good@vaynermedia.com')
+      u.email = 'nope@mailinator.com'
+      u.should_not be_valid
+    end
   end
 
   describe 'passwords' do