diff --git a/lib/valid_email2/address.rb b/lib/valid_email2/address.rb
index c28c3d6..656b93d 100644
--- a/lib/valid_email2/address.rb
+++ b/lib/valid_email2/address.rb
@@ -6,6 +6,8 @@ module ValidEmail2
   class Address
     attr_accessor :address
 
+    ALLOWED_DOMAIN_CHARACTERS_REGEX = /\A[a-z0-9\-.]+\z/i
+
     def initialize(address)
       @parse_error = false
       @raw_address = address
@@ -22,8 +24,14 @@ def valid?
 
       if address.domain && address.address == @raw_address
         domain = address.domain
-        # Valid address needs to have a dot in the domain but not start with a dot
-        !!domain.match(/\./) && !domain.match(/\.{2,}/) && !domain.match(/^\./)
+
+        domain.match(ALLOWED_DOMAIN_CHARACTERS_REGEX) &&
+          # Domain needs to have at least one dot
+          domain.match(/\./) &&
+          # Domain may not have two consecutive dots
+          !domain.match(/\.{2,}/) &&
+          # Domain may not start with a dot
+          !domain.match(/^\./)
       else
         false
       end
diff --git a/spec/valid_email2_spec.rb b/spec/valid_email2_spec.rb
index 4c45277..5bcbd1e 100644
--- a/spec/valid_email2_spec.rb
+++ b/spec/valid_email2_spec.rb
@@ -24,6 +24,11 @@ class BackwardsCompatibleUser < TestModel
   describe "basic validation" do
     subject(:user) { TestUser.new(email: "") }
 
+    it "should not be valid email is valid" do
+      user = TestUser.new(email: "foo@bar123.com")
+      expect(user.valid?).to be_truthy
+    end
+
     it "should be valid when email is empty" do
       expect(user.valid?).to be_truthy
     end
@@ -33,6 +38,13 @@ class BackwardsCompatibleUser < TestModel
       expect(user.valid?).to be_falsey
     end
 
+    it "should be invalid when domain includes invalid characters" do
+      %w(+ _ !).each do |invalid_character|
+        user = TestUser.new(email: "foo@google#{invalid_character}yahoo.com")
+        expect(user.valid?).to be_falsey
+      end
+    end
+
     it "should be invalid when email is malformed" do
       user = TestUser.new(email: "foo@bar")
       expect(user.valid?).to be_falsey