The Ice Mail is an armor that offers protection against Ice based attacks. It is similar in function to the Armor of Water found in other games which have a Water element type instead of an Ice element.
In Castlevania: Symphony of the Night, it gives the normal amount of Defense for an elemental armor, +8, which is twice as much as the Fire Mail, the same as the Lightning Armor and Dark Armor, and 3 less than the Holy Mail.