CAMEL-23222: Filter inbound Camel headers in MailHeaderFilterStrategy

Add setInFilterStartsWith(CAMEL_FILTER_STARTS_WITH) to MailHeaderFilterStrategy to prevent external sources from injecting Camel-prefixed headers on inbound messages.

Author: gnodet

components/camel-mail/src/main/java/org/apache/camel/component/mail/MailHeaderFilterStrategy.java

@@ -28,6 +28,7 @@ protected void initialize() {
         setLowerCase(true);
         // filter headers begin with "Camel" or "org.apache.camel"
         setOutFilterStartsWith(CAMEL_FILTER_STARTS_WITH);
+        setInFilterStartsWith(CAMEL_FILTER_STARTS_WITH);
     }
 
 }