diff --git a/donkey/src/main/java/com/mirth/connect/donkey/model/message/Message.java b/donkey/src/main/java/com/mirth/connect/donkey/model/message/Message.java
index ffac777dbb..63293d21c7 100644
--- a/donkey/src/main/java/com/mirth/connect/donkey/model/message/Message.java
+++ b/donkey/src/main/java/com/mirth/connect/donkey/model/message/Message.java
@@ -117,6 +117,7 @@ public ConnectorMessage getMergedConnectorMessage() {
         if (mergedConnectorMessage == null) {
             mergedConnectorMessage = new ConnectorMessage();
             mergedConnectorMessage.setChannelId(channelId);
+            mergedConnectorMessage.setChannelName(channelName);
             mergedConnectorMessage.setMessageId(messageId);
             mergedConnectorMessage.setServerId(serverId);
             mergedConnectorMessage.setReceivedDate(receivedDate);
@@ -128,6 +129,9 @@ public ConnectorMessage getMergedConnectorMessage() {
             ConnectorMessage sourceConnectorMessage = connectorMessages.get(0);
 
             if (sourceConnectorMessage != null) {
+                if (mergedConnectorMessage.getChannelName() == null) {
+                    mergedConnectorMessage.setChannelName(sourceConnectorMessage.getChannelName());
+                }
                 mergedConnectorMessage.setRaw(sourceConnectorMessage.getRaw());
                 mergedConnectorMessage.setProcessedRaw(sourceConnectorMessage.getProcessedRaw());
                 sourceMap = sourceConnectorMessage.getSourceMap();
diff --git a/donkey/src/test/java/com/mirth/connect/donkey/test/MessageTest.java b/donkey/src/test/java/com/mirth/connect/donkey/test/MessageTest.java
new file mode 100644
index 0000000000..ac05e102d0
--- /dev/null
+++ b/donkey/src/test/java/com/mirth/connect/donkey/test/MessageTest.java
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: MPL-2.0
+// SPDX-FileCopyrightText: 2026 Giovanni Giannola <giogiannola@globalesm.com>
+
+package com.mirth.connect.donkey.test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+
+import java.util.Calendar;
+
+import org.junit.Test;
+
+import com.mirth.connect.donkey.model.message.ConnectorMessage;
+import com.mirth.connect.donkey.model.message.Message;
+import com.mirth.connect.donkey.model.message.Status;
+
+public class MessageTest {
+
+    private static final String CHANNEL_ID = "test-channel-id";
+    private static final String CHANNEL_NAME = "Test Channel";
+    private static final String SERVER_ID = "test-server-id";
+    private static final long MESSAGE_ID = 1L;
+
+    /**
+     * Regression test for issue #309: the channelName variable was not available in the
+     * Postprocessor script because the merged connector message (used to build the postprocessor
+     * scope) never had its channelName populated.
+     */
+    @Test
+    public void mergedConnectorMessageInheritsChannelNameFromSourceConnectorMessage() {
+        Calendar receivedDate = Calendar.getInstance();
+
+        Message message = new Message();
+        message.setMessageId(MESSAGE_ID);
+        message.setChannelId(CHANNEL_ID);
+        message.setServerId(SERVER_ID);
+        message.setReceivedDate(receivedDate);
+
+        ConnectorMessage sourceConnectorMessage = new ConnectorMessage(CHANNEL_ID, CHANNEL_NAME, MESSAGE_ID, 0, SERVER_ID, receivedDate, Status.RECEIVED);
+        message.getConnectorMessages().put(0, sourceConnectorMessage);
+
+        assertEquals(CHANNEL_NAME, message.getMergedConnectorMessage().getChannelName());
+    }
+
+    /**
+     * When the Message itself carries a channelName, it should be propagated to the merged
+     * connector message even if (theoretically) the source connector message did not have one.
+     */
+    @Test
+    public void mergedConnectorMessageUsesMessageChannelNameWhenSet() {
+        Calendar receivedDate = Calendar.getInstance();
+
+        Message message = new Message();
+        message.setMessageId(MESSAGE_ID);
+        message.setChannelId(CHANNEL_ID);
+        message.setChannelName(CHANNEL_NAME);
+        message.setServerId(SERVER_ID);
+        message.setReceivedDate(receivedDate);
+
+        ConnectorMessage sourceConnectorMessage = new ConnectorMessage(CHANNEL_ID, null, MESSAGE_ID, 0, SERVER_ID, receivedDate, Status.RECEIVED);
+        message.getConnectorMessages().put(0, sourceConnectorMessage);
+
+        assertEquals(CHANNEL_NAME, message.getMergedConnectorMessage().getChannelName());
+    }
+
+    /**
+     * With no channel name available anywhere, the merged connector message channelName stays null
+     * (i.e. the fix does not fabricate a value).
+     */
+    @Test
+    public void mergedConnectorMessageChannelNameNullWhenUnavailable() {
+        Calendar receivedDate = Calendar.getInstance();
+
+        Message message = new Message();
+        message.setMessageId(MESSAGE_ID);
+        message.setChannelId(CHANNEL_ID);
+        message.setServerId(SERVER_ID);
+        message.setReceivedDate(receivedDate);
+
+        ConnectorMessage sourceConnectorMessage = new ConnectorMessage(CHANNEL_ID, null, MESSAGE_ID, 0, SERVER_ID, receivedDate, Status.RECEIVED);
+        message.getConnectorMessages().put(0, sourceConnectorMessage);
+
+        assertNull(message.getMergedConnectorMessage().getChannelName());
+    }
+}