I have a hosted VM with a provider, which I've set up mainly as a private mail server. It needs to be protected by some sort of firewall, but there are several to choose from, apart from just writing rules for iptables by hand. I don't think I'll be needing an extreme amount of rules.
Writing rules for iptables is not something I've done in many years, so I was wondering about using either ufw, shorewall or ferm. Has anyone got any experience with either of these? I'm looking for something that is easy to set up and maintain. A pointer to a good guide on any of these would also be much appreciated, especially one that centers on protecting a machine that doesn't serve as a firewall for an entire network, it only has the one interface.