When there is an announced corporate action like a Stock Split or a Special Cash dividend worth more than 25% of the stock's value you may see the dividend dates announced as the Record Date preceding the Ex-Dividend Date. When this occurs the stock will trade with a "Due Bill" attached.
If one were to sell a stock after the record date but before the ex-dividend date, the account would no longer be entitled to the dividend. The shares in such a case would be tagged with a "due bill" which means that the seller is obligated to pay the dividend to the buyer just like an IOU. Likewise, if one were to buy a stock after the record date but before the ex-dividend date (and hold it through the ex-date), the account would be entitled to the dividend from the seller.