diff --git a/post_office/connections.py b/post_office/connections.py
index 435749ee..c6f98df7 100644
--- a/post_office/connections.py
+++ b/post_office/connections.py
@@ -40,6 +40,11 @@ def all(self):
     def close(self):
         for connection in self.all():
             connection.close()
+        # Evict closed connections so the next __getitem__ reopens them.
+        # Keeping closed connections cached breaks backends (e.g. Amazon SES)
+        # whose close() nulls out internal clients — subsequent batches would
+        # hand workers a dead connection and race inside send_messages.
+        self._connections.connections = {}
 
 
 connections = ConnectionHandler()
diff --git a/tests/test_connections.py b/tests/test_connections.py
index d48d0891..2d21dbca 100644
--- a/tests/test_connections.py
+++ b/tests/test_connections.py
@@ -10,3 +10,13 @@ def test_get_connection(self):
         # Ensure ConnectionHandler returns the right connection
         self.assertTrue(isinstance(connections['error'], ErrorRaisingBackend))
         self.assertTrue(isinstance(connections['locmem'], backends.locmem.EmailBackend))
+
+    def test_close_evicts_cache(self):
+        # Ensure connections.close() clears the cache so the next __getitem__
+        # yields a freshly-opened connection. Without this, backends that null
+        # out their client on close() (e.g. Amazon SES) would hand out dead
+        # connections on subsequent batches.
+        first = connections['locmem']
+        connections.close()
+        second = connections['locmem']
+        self.assertIsNot(first, second)
diff --git a/tests/test_models.py b/tests/test_models.py
index b1d62974..e410a54a 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -10,6 +10,7 @@
 from django.core.mail import EmailMessage, EmailMultiAlternatives
 from django.forms.models import modelform_factory
 from django.test import TestCase
+from django.test.utils import override_settings
 from django.utils import timezone
 
 from post_office.models import Email, Log, PRIORITY, STATUS, EmailTemplate, Attachment
@@ -97,9 +98,8 @@ def test_dispatch(self):
         email.dispatch()
         self.assertEqual(mail.outbox[0].subject, 'Test dispatch')
 
+    @override_settings(POST_OFFICE={**settings.POST_OFFICE, 'OVERRIDE_RECIPIENTS': ['override@gmail.com']})
     def test_dispatch_with_override_recipients(self):
-        previous_settings = settings.POST_OFFICE
-        setattr(settings, 'POST_OFFICE', {'OVERRIDE_RECIPIENTS': ['override@gmail.com']})
         email = Email.objects.create(
             to=['to@example.com'],
             from_email='from@example.com',
@@ -109,7 +109,6 @@ def test_dispatch_with_override_recipients(self):
         )
         email.dispatch()
         self.assertEqual(mail.outbox[0].to, ['override@gmail.com'])
-        settings.POST_OFFICE = previous_settings
 
     def test_status_and_log(self):
         """