I am new to the XMPP world and would like to know what are the security concerns that XMPP servers might have, where a firewall such as iptables may play a role in adding additional security. Perhaps there are legacy XMPP servers that require a firewall in comparision to new versions of XMPP servers.
Apart from the typical opening of a port to allow server to server communication or client to server communication, is there anything else, that an XMPP server would benefit from an iptbales firewall (either locally hosted or network based).
I presume the XMPP server would benifit from rate-limiting (DoS control), automatic blacklisting of IP addresses (iptables recent module), layer 7 inspection, perhaps for SPIM like key words or malformed XMPP headers (iptables L-7 filter). Perhaps ensuring the XMPP server, does not initiate connections, rather it listens for connections.
What are the specific threats that can be mitigated by a firewall that helps to secure the XMPP server further?