emails/validators: miscellaneous adjustments (#32435)

* address preferred mx server
 * set connection timeout
 * do not raise validation error on temporary failures
 * add an option to bypass smtp validation
 * catch all dns exceptions

hobo/emails/validators.py

@@ -23,14 +23,14 @@ from django.utils.translation import ugettext_lazy as _
 
 
 def validate_email_address(value):
+    if not settings.HOBO_VALIDATE_EMAIL_WITH_SMTP:
+        return
     email_domain = value.split('@')[-1]
     try:
-        mx_server = dns.resolver.query(email_domain, 'MX')[0].exchange.to_text()
-    except dns.resolver.NXDOMAIN as e:
+        mx_server = sorted(dns.resolver.query(email_domain, 'MX'), key=lambda rdata: rdata.preference)[0].exchange.to_text()
+    except dns.exception.DNSException as e:
         raise ValidationError(_('Error: %s') % str(e))
-    except dns.resolver.NoAnswer as e:
-        raise ValidationError(_('Error: %s') % str(e))
-    smtp = smtplib.SMTP(timeout=30)
+    smtp = smtplib.SMTP(timeout=10)
     try:
         smtp.connect(mx_server)
     except socket.error as e:
@@ -41,11 +41,9 @@ def validate_email_address(value):
         raise ValidationError(_('Error while connecting to %(server)s: %(msg)s') % {'server': mx_server, 'msg': msg})
     smtp.mail('')
     status, msg = smtp.rcpt(value)
-    if status == 250:
-        smtp.quit()
-        return
     smtp.quit()
-    raise ValidationError(_('Email address not found on %s') % mx_server)
+    if status // 100 == 5:
+        raise ValidationError(_('Email address not found on %s') % mx_server)
 
 
 def validate_email_spf(value, strict=False):

hobo/settings.py

@@ -26,6 +26,7 @@ DEBUG = True
 
 ALLOWED_HOSTS = []
 
+HOBO_VALIDATE_EMAIL_WITH_SMTP = True
 ALLOWED_SPF_RECORDS = []
 
 # Application definition

tests/test_emails.py

@@ -22,6 +22,9 @@ def dns_resolver(monkeypatch):
             mx.exchange = mock.create_autospec(name.Name)
             mx.exchange.to_text = mock.MagicMock()
             mx.exchange.to_text.return_value = 'localhost:10025'
+            mx.preference = mock.create_autospec(name.Name)
+            mx.preference.to_text = mock.MagicMock()
+            mx.preference.to_text.return_value = 10
             return [mx]
         if kind == 'TXT':
             txt = mock.create_autospec(TXT)
@@ -86,6 +89,11 @@ def test_validate_email_address_socket_error(dns_resolver, monkeypatch):
     assert 'Error while connecting' in str(e.value)
 
 
+def test_validate_email_address_bypass(settings):
+    settings.HOBO_VALIDATE_EMAIL_WITH_SMTP = False
+    assert validate_email_address('foo') == None
+
+
 def test_invalid_address(client, admin_user):
     client.post('/login/', {'username': 'admin', 'password': 'password'})
     response = client.post('/emails/', {'default_from_email': 'foobar'})