The Mirror Mail is a mid to high ranked heavy armor in Final Fantasy XII that boosts the wearer's Defense by 44 (Zodiac) or 43 (original), Strength by 6—whish is less than the preceding Diamond Armor—and gives a constant Reflect effect to the wearer, bouncing magicks directed onto the target at the enemy. The Mirror Mail is metallic for the purposes of the Magnetize debuff present in the boss battles against Vinuskar (though only available in the shops after the boss) and Ultima.
In the original PlayStation 2 version, the Mirror Mail is sold for 8,100 gil in Phon Coast and Archades. It is found as a treasure in Garamsythe Waterway's No. 11 Channel (Flooded) (50% chance to appear, 90% chance the treasure is Mirror Mail with the Diamond Armlet equipped ), and Cerobi Steppe's The Terraced Bank (50% chance to appear, 80% chance for gil, 50% chance the item treasure is the Mirror Mail without the Diamond Armlet equipped ). It rarely drops from the Mirrorknights; as the knights are plentiful in the Feywood, it is easy to build a chain and potentially farm them for the Mirror Mails, and then sell the yields to make money.
In the updated Zodiac versions, the Mirror Mail is sold for 7,500 gil in Phon Coast and Archades. It is found as a treasure in Phon Coast's Caima Hills (70% chance to appear, 50% chance for gil, 50% chance the item treasure is the Mirror Mail without the Diamond Armlet equipped), and in Tchita Uplands' Sundered Earth (30% chance to appear, 70% chance for gil, 50% chance the item treasure is the Mirror Mail without the Diamond Armlet equipped). It still rarely drops from the Mirrorknights, and is now also rarely stolen from the Cubus in Trial Mode Stage 28.
Mirror Mail is a mid to high level armor giving 44 or 43 Defense depending on version, as well as 6 Strength and a constant Reflect status. The strength bonuses make heavy armor ideal for frontline fighters, though the Mirror Mail offers less Strength than the preceding Diamond Armor, and thus is best not used unless the player wants the Reflect effect, which bounces spells cast onto the character onto enemies. A gun-wielder does not benefit from the strength-boost.
Constant Reflect is useful against magick-spamming enemies who lack the Piercing Magicks augments, and on strategies where the player purposefully reflects spells off their party to multi-cast. The character wearing the Mirror Mail needs to be healed with items, or with white magick while the caster wears the Opal Ring. Alternatives to Mirror Mail are the Ruby Ring accessory, and Self:Reflect and Name:Reflect gambits; the boon to Auto-Reflect from equipment is that the player does not need to use up MP or turns to recasting the spell, and the wearer can be revived from KO with the buff already in place.
In the Zodiac versions, Uhlan, Knight, Time Battlemage, and Foebreaker can equip it, as well as the Black Mage if they unlock Shemhazai; Mirror Mail is only useful to buy if the player has chosen these License Boards for the party. In The Zodiac Age versions, after fighting Belias the player can choose two License Boards per party member and so more characters can benefit from heavy armor, as it is usually a good idea to match jobs that use different types of armor to bolster light armor jobs' strength, and to give more durability to spellcasters. Unlocking the armor for the Black Mage is likely not optimal, as Shemhazai is a late game Esper and likely better used unlocking something else for another job, and there is also another means to bestow Auto-Reflect in the game: Ruby Ring.