Openfire Message queue for blocking smack packet listener

Greetings

I have a scenario in which I use the smack libraries and I implement a packet listener for an xmpp user (‘user 1’).

The messages send from ‘user 2’ to ‘user 1’ takes a long time.

While the packetlistener processes a message ‘user 2’ continues sending messages to ‘user 1’.

‘user 2’ does not receive a response on the consecutive messages.

It is as if the consecutive messages are being thrown away . Is there a queue implementation that keeps the messages stored in case of lengthy operations on the packet listener?

If available can anybody refer me which part of the source code handles message queying .

Is there an existing plugin implementation?

Thanks in advance,

Emmanouil Gkatziouras