ZapMail has been zapped.

Federal Express Corp. is being sued over the use of the name ZapMail for its new two-hour document delivery business by a small Albany, N.Y., firm that claims it has been using the name "Zap" since 1977.

Unfortunately, neither company had bothered to register the name with the federal government, and now the race is on for the legal right to Zap. Federal Express is in the midst of a $1 billion investment program for its two-hour document delivery service.

Zap Legislative Courier Services filed suit in U.S. District Court in Albany claiming that it has used the name "Zap" since 1977.

"By using my company's name in their ads, they have precluded me from expanding my business," said Ed Silverstein, the former longshoreman who runs Zap Legislative Courier Services, still making some deliveries himself. He said his business grosses "around six figures."

"We have been in business for eight years under the name Zap, and we rely on building our reputation through word of mouth," Silverstein said. "Now, when someone says 'try Zap because they're great,' they'll get confused and call Federal Express."

Federal Express officials said they did not know Silverstein's business was using the Zap name when they launched ZapMail last July. They said that, in a country as large as the United States, it is difficult, no matter how thoroughly one checks, to be sure this kind of problem does not occur.

A legal principle to be decided in the case is what right a company such as Zap Legislative Courier Services may claim to the Zap name by using it over time, even if it has not registered the name in Washington. Another issue involves the use of the same name in different markets: Federal Express's ZapMail caters to a national market while Silverstein's firm is a small regional business operating primarily in New York state and Washington, D.C.

Silverstein said he also is upset because Federal Express attorneys misused confidential information about his company. Federal's attorneys, who presumably were calling Silverstein's clients to be sure he was legitimately in the courier business, misidentified themselves during the phone calls. Silverstein's complaint said five of his customers notified him to say they had received strange telephone calls asking about his business.

Federal Express officials said they did not authorize the unusual phone calls and fired the Cincinnati law firm of Wood, Herron & Evans that made the calls for Federal.

Federal Express said it used an outside consulting firm to develop the ZapMail name and a Washington law firm to be sure no one else had prior claim to its use.

With ZapMail, Federal Express is putting together an improved version of facsimile technology using satellites and its fleet of 10,000 vans.