Chainmail wouldn't provide any protection from blunt force; or about as much as your skin.
System wise, I would give each attack a certain amount of force (working with the players strength and weapon weight). Then divide that force depended on both the weapon and the armour. For instance, if I were to slash you with a sword (not hack or stab) I would be focusing my kinetic energy on cutting, but if I struck my opponents chain mail (coverage modifiers go here), all of the cutting damage would be negated, but a certain amount would be transferred to blunt damage. Hacking would transfer more damage to blunt against chain mail, but would be a slower strike, and have a chance of getting stuck on lots of damage (to opponent or armour). So I guess the player should also have a quick, strike-type option, something that could be automated for people with super-lag (don't want to be stabbing with a hammer).
Platemail is the one that gets general damage reduction, from being able to spread the force of any blow of the respective plate. Pierce a hole though and the attacker gets the drive it in for full damage.