Added a keyword argument to normalize which makes it possible to override the default normalizer.

README.md

@@ -8,4 +8,19 @@ from email_normalizer import normalize
 
 # returns alicetestemail@gmail.com
 normalize('Alice.Test.Email+2e16f5091e4c9a1fecd712ad1e019569@gmail.com')
-```
+```
+
+The default normalizer can be overridden if you want to specify your own behavior.
+
+```python
+from email_normalizer import normalize, BaseNormalizer
+
+class MyNormalizer(BaseNormalizer):
+    @classmethod
+    def normalize(cls, local_part, domain):
+        local_part = local_part.split('--')[0]
+        return '{0}@{1}'.format(local_part, domain)
+
+# returns bob@cipher.com
+normalize('Bob--Test@cipher.com', default_normalizer=MyNormalizer)
+```

email_normalizer/__init__.py

@@ -52,7 +52,7 @@ def _get_mx_servers(domain):
         return []
 
 
-def _get_normalizer(domain, resolve):
+def _get_normalizer(domain, resolve, default_normalizer):
     if domain in _domain_normalizers:
         return _domain_normalizers[domain]
 
@@ -62,13 +62,13 @@ def _get_normalizer(domain, resolve):
                 if mx.endswith(service_domain):
                     return normalizer
 
-    return DefaultNormalizer
+    return default_normalizer or DefaultNormalizer
 
 
-def normalize(email, resolve=True):
+def normalize(email, resolve=True, default_normalizer=None):
     local_part, domain = email.lower().split('@')
 
-    return _get_normalizer(domain, resolve).normalize(local_part, domain)
+    return _get_normalizer(domain, resolve, default_normalizer).normalize(local_part, domain)
 
 
 _load_domains()

tests.py

@@ -3,6 +3,7 @@
 import mock
 
 from email_normalizer import normalize, _get_mx_servers, _load_domains
+from email_normalizer import BaseNormalizer
 
 
 class NormalizerTest(unittest.TestCase):
@@ -26,6 +27,14 @@ def test_wrong_domain(self):
     def test_default(self):
         self.assertEqual(normalize('test@domain.com', resolve=False), 'test@domain.com')
 
+    def test_override_default_normalizer(self):
+        class MyNormalizer(BaseNormalizer):
+            @classmethod
+            def normalize(cls, local_part, domain):
+                local_part = local_part.split('+')[0]
+                return '{0}@{1}'.format(local_part, domain)
+        self.assertEqual(normalize('foo+123@bar.com', resolve=False, default_normalizer=MyNormalizer), 'foo@bar.com')
+
     def test_duplicated_domains(self):
         with mock.patch('email_normalizer.google.GoogleNormalizer.domains', ['samedomain.com']), \
                 mock.patch('email_normalizer.yandex.YandexNormalizer.domains', ['samedomain.com']):