Poison pen letter

A poison pen letter (or poisoned 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.

In the United Kingdom, Section 1 of the Malicious Communications Act 1988 covers most cases of poison pen letters.