diff --git a/django_mailbox/migrations/0006_mailbox_last_polling.py b/django_mailbox/migrations/0006_mailbox_last_polling.py
index a46713b..7979428 100644
--- a/django_mailbox/migrations/0006_mailbox_last_polling.py
+++ b/django_mailbox/migrations/0006_mailbox_last_polling.py
@@ -15,6 +15,6 @@ class Migration(migrations.Migration):
         migrations.AddField(
             model_name='mailbox',
             name='last_polling',
-            field=models.DateTimeField(blank=True, null=True, help_text='The time of last successfull polling of message. It is blank for new mailbox or processing email via pipe only.', verbose_name='Last polling'),
+            field=models.DateTimeField(blank=True, help_text='The time of last successful polling for messages.It is blank for new mailboxes and is not set for mailboxes that only receive messages via a pipe.', null=True, verbose_name='Last polling'),
         ),
     ]
diff --git a/django_mailbox/models.py b/django_mailbox/models.py
index 97a1343..89eb0ad 100644
--- a/django_mailbox/models.py
+++ b/django_mailbox/models.py
@@ -100,8 +100,9 @@ class Mailbox(models.Model):
 
     last_polling = models.DateTimeField(
         _(u"Last polling"),
-        help_text=(_("The time of last successfull polling of message. "
-                     "It is blank for new mailbox or processing email via pipe only.")),
+        help_text=(_("The time of last successful polling for messages."
+                     "It is blank for new mailboxes and is not set for "
+                     "mailboxes that only receive messages via a pipe.")),
         blank=True,
         null=True
     )