Wearer is immune to Retribution Damage (RD). However, Retribution Damage with a damage-type of Eldritch cannot be negated. Nothing can mitigate Eldritch damage.
Retribution Damage occurs when a spell or item deals damage to an attacker on a successful hit.
Note: Misfire damage from a “blunder” weapon is not Retribution Damage and is not negated by this shirt.