Windstar Cruises, Seattle, will market its maritime getaways to more than 18,000 U.S. travel agents through an e-mail direct marketing program, the company said yesterday. The agents signed up online to receive the e-mail broadcast service, called eSail, which was developed by e-mail database and transmission company e-Marketing Inc., Marietta, GA. The electronic messages will peddle special offers, group booking incentives, links to the cruise company's home page and other products. Future plans call for an archive that will store Windstar product information that can be e-mailed instantly to travel agents who request it. Other travel operators will be included in the broadcasts, but Windstar will receive preferred placement in the messages, the company said.