Greenmail refers to the agreement between a large shareholder and a company in which the shareholder agrees to sell his stock back to the company, usually at a premium, in exchange for the promise not to seek control of the company for a specified period of time. Antigreenmail provisions prevent such arrangements unless the same repurchase offer is made to all shareholders or approved by shareholder vote. There are some states that have antigreenmail laws.
A provision in a corporate charter forbidding the payment of a bon voyage bonus without the approval of a given majority of shareholders. Greenmailing is a practice in which a corporate raider buys a large amount of stock from another publicly-traded company and forces the latter to buy back the stock at a substantial premium in order to avoid a takeover. One refers to this buyback as the bon voyage bonus, as this enables the company to be left alone by the greenmailer. An anti-greenmail provision discourages corporate raiders from greenmailing in the first place as it makes the bon voyage bonus more difficult to receive, which may result in the greenmailer becoming stuck with ownership of shares he/she does not actually want.