diff --git a/tests/test_smtp_check.py b/tests/test_smtp_check.py
index 5266197..26b3747 100644
--- a/tests/test_smtp_check.py
+++ b/tests/test_smtp_check.py
@@ -1,38 +1,100 @@
-from smtplib import SMTP
+from smtplib import SMTPServerDisconnected
+from socket import timeout
 from unittest.case import TestCase
 from unittest.mock import patch
 
-from validate_email.exceptions import SMTPMessage, SMTPTemporaryError
-from validate_email.smtp_check import _SMTPChecker
+from validate_email.email_address import EmailAddress
+from validate_email.exceptions import (
+    AddressNotDeliverableError, SMTPCommunicationError, SMTPTemporaryError)
+from validate_email.smtp_check import _SMTPChecker, smtp_check
 
 
-class SMTPCheckerTest(TestCase):
-    'Checking the `_SMTPChecker` class methods.'
+class SMTPMock(_SMTPChecker):
+    """
+    Mock replacement for the SMTP connection.
 
-    @patch.object(target=SMTP, attribute='connect')
-    def test_connect_raises_serverdisconnected(self, mock_connect):
-        'Connect raises `SMTPTemporaryError`.'
-        mock_connect.side_effect = OSError('test message')
-        checker = _SMTPChecker(
-            local_hostname='localhost', timeout=5, debug=False,
-            sender='test@example.com', recip='test@example.com')
-        with self.assertRaises(SMTPTemporaryError) as exc:
-            checker.check(hosts=['testhost'])
-        self.assertDictEqual(exc.exception.error_messages, {
-            'testhost': SMTPMessage(
-                command='connect', code=451, text='test message')
-        })
+    Instead of really communicating with an SMTP server, this class
+    works with predefined fake responses. By default, the responses
+    emulate a successful SMTP conversation, but it can be turned into an
+    unsuccessful one by patching the `reply` dictionary.
+    """
+    reply = {
+        None: (220, b'Welcome'),
+        "EHLO": (502, b'Please use HELO'),
+        'HELO': (220, b'HELO successful'),
+        'MAIL': (250, b'MAIL FROM successful'),
+        'RCPT': (250, b'RCPT TO successful'),
+        'QUIT': (221, b'QUIT successful'),
+    }
 
-    @patch.object(target=SMTP, attribute='connect')
-    def test_connect_with_error(self, mock_connect):
-        'Connect raises `SMTPTemporaryError`.'
-        checker = _SMTPChecker(
-            local_hostname='localhost', timeout=5, debug=False,
-            sender='test@example.com', recip='test@example.com')
-        mock_connect.return_value = (400, b'test delay message')
-        with self.assertRaises(SMTPTemporaryError) as exc:
-            checker.check(hosts=['testhost'])
-        self.assertDictEqual(exc.exception.error_messages, {
-            'testhost': SMTPMessage(
-                command='connect', code=400, text='test delay message')
-        })
+    last_command = None
+
+    def _get_socket(self, host, port, timeout):
+        return None
+
+    def send(self, s):
+        self.last_command = s[:4].upper()
+
+    def getreply(self):
+        if isinstance(self.reply[self.last_command], Exception):
+            self.close()
+            raise self.reply[self.last_command]
+        return self.reply[self.last_command]
+
+
+class SMTPCheckTest(TestCase):
+    'Collection of tests the `smtp_check` method.'
+
+    # All the possible ways to fail we want to test, listed as tuples
+    # containing (command, reply, expected exception).
+    failures = [
+        # Timeout on connection
+        (None, timeout(), SMTPTemporaryError),
+        # Connection unexpectedly closed during any stage
+        (None, SMTPServerDisconnected('Test'), SMTPTemporaryError),
+        ('EHLO', SMTPServerDisconnected('Test'), SMTPTemporaryError),
+        ('HELO', SMTPServerDisconnected('Test'), SMTPTemporaryError),
+        ('MAIL', SMTPServerDisconnected('Test'), SMTPTemporaryError),
+        ('RCPT', SMTPServerDisconnected('Test'), SMTPTemporaryError),
+        # Temporary error codes
+        (None, (421, b'Connect failed'), SMTPTemporaryError),
+        ('HELO', (421, b'HELO failed'), SMTPTemporaryError),
+        ('MAIL', (451, b'MAIL FROM failed'), SMTPTemporaryError),
+        ('RCPT', (451, b'RCPT TO failed'), SMTPTemporaryError),
+        # Permanent error codes
+        (None, (554, b'Connect failed'), SMTPCommunicationError),
+        ('HELO', (504, b'HELO failed'), SMTPCommunicationError),
+        ('MAIL', (550, b'MAIL FROM failed'), SMTPCommunicationError),
+        ('RCPT', (550, b'RCPT TO failed'), AddressNotDeliverableError),
+    ]
+
+    @patch(target='validate_email.smtp_check._SMTPChecker', new=SMTPMock)
+    def test_smtp_success(self):
+        'Succeeds on successful SMTP conversation'
+        self.assertTrue(
+            smtp_check(
+                email_address=EmailAddress('alice@example.com'),
+                mx_records=['smtp.example.com'],
+            )
+        )
+
+    def _test_one_smtp_failure(self, cmd, reply, exception):
+        with patch.dict(in_dict=SMTPMock.reply, values={cmd: reply}):
+            with self.assertRaises(exception) as context:
+                smtp_check(
+                    email_address=EmailAddress('alice@example.com'),
+                    mx_records=['smtp.example.com'],
+                )
+            if isinstance(reply, tuple):
+                error_messages = context.exception.error_messages
+                error_info = error_messages['smtp.example.com']
+                self.assertEqual(error_info.command[:4].upper(), cmd or 'CONN')
+                self.assertEqual(error_info.code, reply[0])
+                self.assertEqual(error_info.text, reply[1].decode())
+
+    @patch(target='validate_email.smtp_check._SMTPChecker', new=SMTPMock)
+    def test_smtp_failure(self):
+        'Fails on unsuccessful SMTP conversation.'
+        for cmd, reply, exception in self.failures:
+            with self.subTest(cmd=cmd, reply=reply):
+                self._test_one_smtp_failure(cmd, reply, exception)