So unfortunately, I've been tasked with setting up an Ubuntu server to send and receive email (amongst other things). My friend is hosting the Ubuntu VM on his box, but has only done limited setup.

4 0 0 ACCEPT tcp -- any any 10.100.100.0/24 anywhere state NEW tcp dpt:ssh 5 1 64 ACCEPT tcp -- any any anywhere anywhere state NEW tcp dpt:smtp 6 730 103K REJECT all -- any any anywhere anywhere ...