Are you are running WSO2ESB and receiving this error "AnonymousEndpoint has been marked for SUSPENSION, but no further retries remain" printed on console? This error occurs when trying to send the message again. If this error prints in the console repetitively, then WSO2ESB is trying send messages repetitively. So inspect "<syn:send/>" elements in the synapse config, and it may not be required.
Here is a scenario I ran into.
I am using WSO2ESB-2.1.1(or later) and trying to re-use an old synapse configuration. I am trying to use a proxy service.
In the synapse configuration, I have target endpoint specified in the proxy service, so <syn:send> is not required according to new rules. So when I removed <syn:send/> from the synapse config's inSequence it worked beautifully. BTW .. you have to restart the server.