diff --git a/sdk/eventhub/azure-eventhub/CHANGELOG.md b/sdk/eventhub/azure-eventhub/CHANGELOG.md
index a7d4e0fb075e..57074132f668 100644
--- a/sdk/eventhub/azure-eventhub/CHANGELOG.md
+++ b/sdk/eventhub/azure-eventhub/CHANGELOG.md
@@ -8,6 +8,8 @@
 
 ### Bugs Fixed
 
+- Fixed a bug that `EventHubProducerClient` could be reopened for sending events instead of encountering with `KeyError` when the client is previously closed (issue #21849).
+
 ### Other Changes
 
 ## 5.6.1 (2021-10-06)
diff --git a/sdk/eventhub/azure-eventhub/azure/eventhub/_producer_client.py b/sdk/eventhub/azure-eventhub/azure/eventhub/_producer_client.py
index 39f44773202d..89e9b0cfcfd9 100644
--- a/sdk/eventhub/azure-eventhub/azure/eventhub/_producer_client.py
+++ b/sdk/eventhub/azure-eventhub/azure/eventhub/_producer_client.py
@@ -17,7 +17,11 @@
 from ._common import EventDataBatch, EventData
 
 if TYPE_CHECKING:
-    from azure.core.credentials import TokenCredential, AzureSasCredential, AzureNamedKeyCredential
+    from azure.core.credentials import (
+        TokenCredential,
+        AzureSasCredential,
+        AzureNamedKeyCredential,
+    )
 
 SendEventTypes = List[Union[EventData, AmqpAnnotatedMessage]]
 
@@ -143,7 +147,10 @@ def _start_producer(self, partition_id, send_timeout):
                 or cast(EventHubProducer, self._producers[partition_id]).closed
             ):
                 self._producers[partition_id] = self._create_producer(
-                    partition_id=partition_id, send_timeout=send_timeout
+                    partition_id=(
+                        None if partition_id == ALL_PARTITIONS else partition_id
+                    ),
+                    send_timeout=send_timeout,
                 )
 
     def _create_producer(self, partition_id=None, send_timeout=None):
@@ -261,14 +268,21 @@ def send_batch(self, event_data_batch, **kwargs):
 
         if isinstance(event_data_batch, EventDataBatch):
             if partition_id or partition_key:
-                raise TypeError("partition_id and partition_key should be None when sending an EventDataBatch "
-                                "because type EventDataBatch itself may have partition_id or partition_key")
+                raise TypeError(
+                    "partition_id and partition_key should be None when sending an EventDataBatch "
+                    "because type EventDataBatch itself may have partition_id or partition_key"
+                )
             to_send_batch = event_data_batch
         else:
-            to_send_batch = self.create_batch(partition_id=partition_id, partition_key=partition_key)
-            to_send_batch._load_events(event_data_batch)  # pylint:disable=protected-access
+            to_send_batch = self.create_batch(
+                partition_id=partition_id, partition_key=partition_key
+            )
+            to_send_batch._load_events(  # pylint:disable=protected-access
+                event_data_batch
+            )
         partition_id = (
-            to_send_batch._partition_id or ALL_PARTITIONS  # pylint:disable=protected-access
+            to_send_batch._partition_id  # pylint:disable=protected-access
+            or ALL_PARTITIONS
         )
 
         if len(to_send_batch) == 0:
@@ -400,8 +414,8 @@ def close(self):
 
         """
         with self._lock:
-            for producer in self._producers.values():
-                if producer:
-                    producer.close()
-            self._producers = {}
+            for pid in self._producers:
+                if self._producers[pid]:
+                    self._producers[pid].close()  # type: ignore
+                self._producers[pid] = None
         super(EventHubProducerClient, self)._close()
diff --git a/sdk/eventhub/azure-eventhub/azure/eventhub/aio/_producer_client_async.py b/sdk/eventhub/azure-eventhub/azure/eventhub/aio/_producer_client_async.py
index 728902461d60..79077f4e3d20 100644
--- a/sdk/eventhub/azure-eventhub/azure/eventhub/aio/_producer_client_async.py
+++ b/sdk/eventhub/azure-eventhub/azure/eventhub/aio/_producer_client_async.py
@@ -19,7 +19,7 @@
 
 if TYPE_CHECKING:
     from azure.core.credentials_async import AsyncTokenCredential
-    from uamqp.constants import TransportType # pylint: disable=ungrouped-imports
+    from uamqp.constants import TransportType  # pylint: disable=ungrouped-imports
 
 SendEventTypes = List[Union[EventData, AmqpAnnotatedMessage]]
 
@@ -80,7 +80,9 @@ def __init__(
         self,
         fully_qualified_namespace: str,
         eventhub_name: str,
-        credential: Union["AsyncTokenCredential", AzureSasCredential, AzureNamedKeyCredential],
+        credential: Union[
+            "AsyncTokenCredential", AzureSasCredential, AzureNamedKeyCredential
+        ],
         **kwargs
     ) -> None:
         super(EventHubProducerClient, self).__init__(
@@ -145,7 +147,10 @@ async def _start_producer(
                 or cast(EventHubProducer, self._producers[partition_id]).closed
             ):
                 self._producers[partition_id] = self._create_producer(
-                    partition_id=partition_id, send_timeout=send_timeout
+                    partition_id=(
+                        None if partition_id == ALL_PARTITIONS else partition_id
+                    ),
+                    send_timeout=send_timeout,
                 )
 
     def _create_producer(
@@ -294,18 +299,25 @@ async def send_batch(
 
         if isinstance(event_data_batch, EventDataBatch):
             if partition_id or partition_key:
-                raise TypeError("partition_id and partition_key should be None when sending an EventDataBatch "
-                                "because type EventDataBatch itself may have partition_id or partition_key")
+                raise TypeError(
+                    "partition_id and partition_key should be None when sending an EventDataBatch "
+                    "because type EventDataBatch itself may have partition_id or partition_key"
+                )
             to_send_batch = event_data_batch
         else:
-            to_send_batch = await self.create_batch(partition_id=partition_id, partition_key=partition_key)
-            to_send_batch._load_events(event_data_batch)  # pylint:disable=protected-access
+            to_send_batch = await self.create_batch(
+                partition_id=partition_id, partition_key=partition_key
+            )
+            to_send_batch._load_events(  # pylint:disable=protected-access
+                event_data_batch
+            )
 
         if len(to_send_batch) == 0:
             return
 
         partition_id = (
-            to_send_batch._partition_id or ALL_PARTITIONS  # pylint:disable=protected-access
+            to_send_batch._partition_id  # pylint:disable=protected-access
+            or ALL_PARTITIONS
         )
         try:
             await cast(EventHubProducer, self._producers[partition_id]).send(
@@ -431,7 +443,9 @@ async def close(self) -> None:
 
         """
         async with self._lock:
-            for producer in self._producers.values():
-                if producer:
-                    await producer.close()
+            for pid in self._producers:
+                if self._producers[pid] is not None:
+                    await self._producers[pid].close()  # type: ignore
+                self._producers[pid] = None
+
         await super(EventHubProducerClient, self)._close_async()
diff --git a/sdk/eventhub/azure-eventhub/tests/livetest/asynctests/test_send_async.py b/sdk/eventhub/azure-eventhub/tests/livetest/asynctests/test_send_async.py
index 4eac51006c9f..e2c281d3a32a 100644
--- a/sdk/eventhub/azure-eventhub/tests/livetest/asynctests/test_send_async.py
+++ b/sdk/eventhub/azure-eventhub/tests/livetest/asynctests/test_send_async.py
@@ -189,15 +189,34 @@ async def test_send_and_receive_small_body_async(connstr_receivers, payload):
 async def test_send_partition_async(connstr_receivers):
     connection_str, receivers = connstr_receivers
     client = EventHubProducerClient.from_connection_string(connection_str)
+
+    async with client:
+        batch = await client.create_batch()
+        batch.add(EventData(b"Data"))
+        await client.send_batch(batch)
+
     async with client:
         batch = await client.create_batch(partition_id="1")
         batch.add(EventData(b"Data"))
         await client.send_batch(batch)
 
     partition_0 = receivers[0].receive_message_batch(timeout=5000)
-    assert len(partition_0) == 0
     partition_1 = receivers[1].receive_message_batch(timeout=5000)
-    assert len(partition_1) == 1
+    assert len(partition_0) + len(partition_1) == 2
+
+    async with client:
+        batch = await client.create_batch()
+        batch.add(EventData(b"Data"))
+        await client.send_batch(batch)
+
+    async with client:
+        batch = await client.create_batch(partition_id="1")
+        batch.add(EventData(b"Data"))
+        await client.send_batch(batch)
+
+    partition_0 = receivers[0].receive_message_batch(timeout=5000)
+    partition_1 = receivers[1].receive_message_batch(timeout=5000)
+    assert len(partition_0) + len(partition_1) == 2
 
 
 @pytest.mark.liveTest
diff --git a/sdk/eventhub/azure-eventhub/tests/livetest/synctests/test_send.py b/sdk/eventhub/azure-eventhub/tests/livetest/synctests/test_send.py
index 6bc42d0ea3eb..0872b55ae85f 100644
--- a/sdk/eventhub/azure-eventhub/tests/livetest/synctests/test_send.py
+++ b/sdk/eventhub/azure-eventhub/tests/livetest/synctests/test_send.py
@@ -206,15 +206,34 @@ def test_send_and_receive_small_body(connstr_receivers, payload):
 def test_send_partition(connstr_receivers):
     connection_str, receivers = connstr_receivers
     client = EventHubProducerClient.from_connection_string(connection_str)
+
+    with client:
+        batch = client.create_batch()
+        batch.add(EventData(b"Data"))
+        client.send_batch(batch)
+
     with client:
         batch = client.create_batch(partition_id="1")
         batch.add(EventData(b"Data"))
         client.send_batch(batch)
 
     partition_0 = receivers[0].receive_message_batch(timeout=5000)
-    assert len(partition_0) == 0
     partition_1 = receivers[1].receive_message_batch(timeout=5000)
-    assert len(partition_1) == 1
+    assert len(partition_0) + len(partition_1) == 2
+
+    with client:
+        batch = client.create_batch()
+        batch.add(EventData(b"Data"))
+        client.send_batch(batch)
+
+    with client:
+        batch = client.create_batch(partition_id="1")
+        batch.add(EventData(b"Data"))
+        client.send_batch(batch)
+
+    partition_0 = receivers[0].receive_message_batch(timeout=5000)
+    partition_1 = receivers[1].receive_message_batch(timeout=5000)
+    assert len(partition_0) + len(partition_1) == 2
 
 
 @pytest.mark.liveTest