A Washington state Internet service provider (ISP) has filed a $6 million (£3.7 million) anti-spam lawsuit against a Fortune 500 company, alleging it disabled the ISP's mail servers by sending thousands of e-mail advertisements to subscribers. The ISP, Connect Northwest claims that CTX Mortgage sent 5,800 unsolicited e-mail ads to its subscribers on April 8 and 9, causing Connect Northwest to have to briefly shut down its service to deal with clogged servers. Connect Northwest's attorney, Brady R. Johnson, said in a statement that CTX apparently generated the messages automatically with software that produces lists of probable user names, combined with the ISP's domain name. "They figure that every ISP has a user named Dan, but to get to 'Dan,' it also tries 'Dal' and 'Dam,' Johnson said in a statement. The messages also used misleading subject lines and headers, in violation of the state law, he said. The mail overload was intensified when the ISP's e-mail system automatically generated "message undeliverable" notifications for each erroneous e-mail address CTX's software produced, Johnson said. The lawsuit, filed Monday in Skagit County Superior Court in Mount Vernon, is among the first to target a large company using Washington state's anti-spam law. CTX is a subsidiary of Dallas-based Centex, a construction and financial services conglomerate with 10,000 workers. CTX officials said in a statement issued Wednesday they are investigating how the e-mails came to be sent. "What we have learned is that the e-mails in question represent an isolated incident involving an outside vendor," CTX officials said. "CTX takes the anti-spamming laws seriously and immediately stopped the activity pending investigation of the matter." The law prohibits sending unsolicited commercial e-mail with misleading subject lines, false return addresses and false headers. It calls for $1,000 (£619) in fines for each illegal message. Several other lawsuits have already been filed in Washington state under the law, most against small firms or individuals. None of those suits has yet come to trial. Neither Johnson nor CTX executives could be reached for further comment Thursday.