Poison pen letter

Malicious letter, usually anonymous

A poison pen letter is a letter or note containing unpleasant, abusive, or malicious statements or accusations about the recipient or a third party. It is usually sent anonymously, often by employing the ransom note effect to avoid exposing the author's handwriting. Poison pen letters are usually composed and sent to upset the recipient, and differ from blackmail, which is intended to obtain something from the recipient. The reference to poison is figurative rather than literal.

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