Tighten parser email validation with regression tests

tests/parser_test.py

@@ -56,6 +56,11 @@ class ParserTest(unittest.TestCase):
         self.assertIsNone(p("no at sign at all"))
         self.assertIsNone(p("plain text line:with:colons"))
         self.assertIsNotNone(p("user%40domain.com:password"))  # %40 still becomes '@'
+        # Symbol-laden local parts are rejected by the strict ASCII regex.
+        self.assertIsNone(p("[email protected]:12abcd"))
+        self.assertIsNone(p("[email protected]:pw"))
+        self.assertIsNone(p("[email protected]:pw"))  # '+' not allowed by the regex
+        self.assertIsNotNone(p("[email protected]:pw"))
         self.assertIsNotNone(
             p("[email protected]:[email protected]:victory")
         )