When we have multiple site masters, a multicast is relayed to all other sites by the site master (when relay_multicasts is true).
When we have multiple site masters, this results in a message M being delivered to every site N times, where N is the number of site masters (max_site_masters).
This could be changed as follows:

• A site master creates a hash H from the message (e.g. sender's address)
• H mod number of site masters yields the rank of the site master to relay the multicast
  -> Only a single site master relays the multicast; the one with the computed rank