Corrected domain max length for EmailValidator; refs #20631.

Thanks MarkusH for the report.

django/core/validators.py

@@ -124,9 +124,9 @@ class EmailValidator(object):
         r'|^"([\001-\010\013\014\016-\037!#-\[\]-\177]|\\[\001-\011\013\014\016-\177])*"$)',  # quoted-string
         re.IGNORECASE)
     domain_regex = re.compile(
-        # max length of the domain is 251: 254 (max email length) minus one
-        # period and two characters for the TLD.
-        r'(?:[A-Z0-9](?:[A-Z0-9-]{0,249}[A-Z0-9])?\.)+(?:[A-Z]{2,6}|[A-Z0-9-]{2,}(?<!-))$',
+        # max length of the domain is 249: 254 (max email length) minus one
+        # period, two characters for the TLD, @ sign, & one character before @.
+        r'(?:[A-Z0-9](?:[A-Z0-9-]{0,247}[A-Z0-9])?\.)+(?:[A-Z]{2,6}|[A-Z0-9-]{2,}(?<!-))$',
         re.IGNORECASE)
     literal_regex = re.compile(
         # literal form, ipv4 or ipv6 address (SMTP 4.1.3)

tests/validators/tests.py

@@ -66,9 +66,9 @@ TEST_DATA = (
     (validate_email, '"\\\011"@here.com', None),
     (validate_email, '"\\\012"@here.com', ValidationError),
     (validate_email, 'trailingdot@shouldfail.com.', ValidationError),
-    # Max length of domain name in email is 251 (see validator for calculation)
-    (validate_email, 'a@%s.com' % ('a' * 251), None),
-    (validate_email, 'a@%s.com' % ('a' * 252), ValidationError),
+    # Max length of domain name in email is 249 (see validator for calculation)
+    (validate_email, 'a@%s.us' % ('a' * 249), None),
+    (validate_email, 'a@%s.us' % ('a' * 250), ValidationError),
 
     (validate_slug, 'slug-ok', None),
     (validate_slug, 'longer-slug-still-ok', None),