title: Under what circumstances do ZeroMQ sockets drop or fail to deliver messages?
body: <p>Is there some sort of a specification or other explanation that describes the normal cases where you can expect a message sent on a ZeroMQ socket to not be received by ( all ) the listening processes, for each communication type?</p>
  
  <p>For example I have an experimental program which basically assumes that all subscribers to a <code>PUB</code> socket receive all messages sent on that socket ( after an initialization handshake ).  I would like to understand the cases where that assumption may be false.  Thanks, and sorry if this has already been asked.</p>