I don't recall if there is any code-side work to be done implementing new items. (I also don't know if adding new items is a great idea in general. Mucks with balance.) But, I'm half asleep and apparently I just pieced together some script:
Config SWIFT_MAIL;
{
Possibility = 10;
StrengthModifier = 100;
DefaultSize = 75;
DefaultMainVolume = 2000;
BitmapPos = 16, 96;
Adjective = "lightweight";
NameSingular = "chain mail";
MainMaterialConfig = { 9, TIN, BRONZE, IRON, STEEL, METEORIC_STEEL, ARCANITE, MITHRIL, OMMEL_BONE, OMMEL_TOOTH; }
MaterialConfigChances = { 9, 150, 450, 300, 150, 25, 20, 25, 10, 5; }
InElasticityPenaltyModifier = 5;
TorsoArmorBitmapPos = 32, 432;
ArmArmorBitmapPos = 64, 432;
AthleteArmArmorBitmapPos = 64, 464;
LegArmorBitmapPos = 0, 432;
EnchantmentPlusChance = 5;
}
It's a lightweight chain mail. 80% of the armor rating with half the penalties. Substantially more rare, however, and less likely to be enchanted. Also, it sometimes spawns made of tin...
Now, I'm going to stop making contributions and go to bed.