The scenario is the following: A number of messages need to be written to a specified file. The messages arrive fine up to the FileMessageDispatcher but once they are written, some messages are missing from the file. Note that not the same amount of messages are lost. Some times all messages arrive fine. This problem probably occurs due to thread interference, with the output of one thread being overwritten by that of another. Synchronizing the doDispatch() method seems to solve the problem. The code modification suggested is as seen below: synchronized (mutex) { FileOutputStream fos = (FileOutputStream)connector.getOutputStream(event.getEndpoint(), message); if (event.getMessage().getStringProperty(FileConnector.PROPERTY_FILENAME, null) == null) { event.getMessage().setStringProperty(FileConnector.PROPERTY_FILENAME, message.getStringProperty(FileConnector.PROPERTY_FILENAME, "")); } try { fos.write(buf); } finally { fos.close(); } } The mutex is declared as follows: private final static Object mutex = new Object(); Any thoughts on this?