wso2 How to unblock messageProcessor - wso2-esb

Question

I have used a message Processor to call an end Point and make a guaranteed delivery.
Sometimes it happens that a buggy message (incompatible data type with the end point WS) what causes ERROR HTTP SC: 500
all the follow up messages (this time correct ones) are stuck due to the first blocking message.
How to unblock the message processor?
how to delete it from the queue? possibly is there a way how to correct it?
This is very dangerous if it happens in the production.
thank you!
message processor
<?xml version="1.0" encoding="UTF-8"?>
<messageProcessor
class="org.apache.synapse.message.processor.impl.forwarder.ScheduledMessageForwardingProcessor"
messageStore="SAPMoveMaterialOriginalMsgStore"
name="SAPMoveMaterialMessageProcessor"
targetEndpoint="SAPmaterialMoveProxyService" xmlns="http://ws.apache.org/ns/synapse">
<parameter name="client.retry.interval">900000</parameter>
<parameter name="throttle">false</parameter>
<parameter name="max.delivery.attempts">50</parameter>
<parameter name="member.count">1</parameter>
<parameter name="message.processor.reply.sequence">handleSAPResponse</parameter>
<parameter name="message.processor.fault.sequence">fault</parameter>
<parameter name="max.delivery.drop">Enabled</parameter>
<parameter name="interval">1000</parameter>
<parameter name="is.active">true</parameter>
</messageProcessor>
The end point
<?xml version="1.0" encoding="UTF-8"?>
<endpoint name="zsap_material_move" xmlns="http://ws.apache.org/ns/synapse">
<address trace="disable" uri="http://r3cr1.echternach.ieeintern:8020/sap/bc/srt/rfc/sap/zsap_material_move">
<timeout>
<duration>60000</duration>
</timeout>
</address>
</endpoint>

Answer 1

Do not send the message directly to your endpoint, but to a proxy service where you define your own mediation and decide what kind of response to send back to the Message Processor

Answer 2

In the Message Forwarding processor, It you do not want to retry any messages which returns HTTP 500 you can specify "Non retry http status codes" to avoid. Also if you set the "Maximum redelivery attempts" property and set "Drop message after maximum delivery attempts" to true it will drop the message without blocking the processor. Also in the Fault sequence you can decide on the mediation login you need to perform on the Faulty message. You can refer the following screen for this.