Add support for null MX rfc7505

CHANGELOG.md

@@ -1,3 +1,6 @@
+## unreleased
+* support null MX rfc7505 #206
+
 ## Version 4.0.6
 * Remove false positives https://github.com/micke/valid_email2/pull/200
 * Remove unused default option https://github.com/micke/valid_email2/pull/201

lib/valid_email2/address.rb

@@ -91,12 +91,14 @@ def blacklisted?
 
     def valid_mx?
       return false unless valid?
+      return false if null_mx?
 
       mx_or_a_servers.any?
     end
 
     def valid_strict_mx?
       return false unless valid?
+      return false if null_mx?
 
       mx_servers.any?
     end
@@ -138,6 +140,10 @@ def mx_servers
       end
     end
 
+    def null_mx?
+      mx_servers.length == 1 && mx_servers.first.preference == 0 && mx_servers.first.exchange.length == 0
+    end
+
     def mx_or_a_servers
       @mx_or_a_servers ||= Resolv::DNS.open do |dns|
         dns.timeouts = @dns_timeout

spec/valid_email2_spec.rb

@@ -255,6 +255,11 @@ def set_whitelist
       user = TestUserMX.new(email: "[email protected]")
       expect(user.valid?).to be_falsey
     end
+
+    it "is invalid if a null mx is found" do
+      user = TestUserMX.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
   end
 
   describe "with strict mx validation" do
@@ -272,6 +277,11 @@ def set_whitelist
       user = TestUserStrictMX.new(email: "[email protected]")
       expect(user.valid?).to be_falsey
     end
+
+    it "is invalid if a null mx is found" do
+      user = TestUserMX.new(email: "[email protected]")
+      expect(user.valid?).to be_falsey
+    end
   end
 
   describe "with dotted validation" do