[backport camel-4.18.x] CAMEL-23891: camel-mail - filter Camel internal headers in MimeMultipartDataFormat unmarshal

components/camel-mail/src/main/java/org/apache/camel/dataformat/mime/multipart/MimeMultipartDataFormat.java

@@ -50,8 +50,10 @@
 import org.apache.camel.attachment.Attachment;
 import org.apache.camel.attachment.AttachmentMessage;
 import org.apache.camel.attachment.DefaultAttachment;
+import org.apache.camel.spi.HeaderFilterStrategy;
 import org.apache.camel.spi.annotations.Dataformat;
 import org.apache.camel.support.DefaultDataFormat;
+import org.apache.camel.support.DefaultHeaderFilterStrategy;
 import org.apache.camel.support.ExchangeHelper;
 import org.apache.camel.support.MessageHelper;
 import org.apache.camel.util.IOHelper;
@@ -72,6 +74,7 @@ public class MimeMultipartDataFormat extends DefaultDataFormat {
     private String includeHeaders;
     private Pattern includeHeadersPattern;
     private boolean binaryContent;
+    private final HeaderFilterStrategy headerFilterStrategy = new DefaultHeaderFilterStrategy();
 
     public String getMultipartSubType() {
         return multipartSubType;
@@ -282,6 +285,12 @@ private void copyNonStandardHeaders(MimeBodyPart mimeMessage, Message camelMessa
         while (headersEnum.hasMoreElements()) {
             Object ho = headersEnum.nextElement();
             if (ho instanceof Header header) {
+                // filter Camel internal headers (Camel*) instead of copying them verbatim from the external
+                // MIME headers, consistent with the inbound HeaderFilterStrategy applied by the mail consumer
+                if (headerFilterStrategy.applyFilterToExternalHeaders(header.getName(), header.getValue(),
+                        camelMessage.getExchange())) {
+                    continue;
+                }
                 camelMessage.setHeader(header.getName(), header.getValue());
             }
         }

components/camel-mail/src/test/java/org/apache/camel/dataformat/mime/multipart/MimeMultipartDataFormatTest.java

@@ -406,6 +406,27 @@ public void marhsalUnmarshalInlineHeaders() throws IOException {
         assertEquals("also there", out.getMessage().getHeader("x-bar"));
     }
 
+    @Test
+    public void unmarshalInlineHeadersFiltersCamelInternalHeaders() {
+        // Camel-internal headers (Camel*, case-insensitive) present in the external MIME headers must not be
+        // copied onto the Camel message; ordinary application headers still pass through. This matches the
+        // inbound HeaderFilterStrategy applied by the mail consumer.
+        String mime = "CamelFoo: blocked\r\n"
+                      + "camelBar: blocked\r\n"
+                      + "CAMELBaz: blocked\r\n"
+                      + "X-Normal: keep-me\r\n"
+                      + "Content-Type: text/plain\r\n"
+                      + "\r\n"
+                      + "Body text";
+        in.setBody(mime);
+        Exchange out = template.send("direct:unmarshalonlyinlineheaders", exchange);
+        assertNotNull(out.getMessage());
+        assertEquals("keep-me", out.getMessage().getHeader("X-Normal"));
+        assertNull(out.getMessage().getHeader("CamelFoo"));
+        assertNull(out.getMessage().getHeader("camelBar"));
+        assertNull(out.getMessage().getHeader("CAMELBaz"));
+    }
+
     @Test
     public void unmarshalRelated() throws IOException {
         in.setBody(new File("src/test/resources/multipart-related.txt"));